remove nested encoding

[DavidBadura]

I noticed that we serialize every single header as json, and at the end save the whole thing again in the db as json. We can make this more optimized by no longer serializing all individual headers as json and only in the DB.

The typehints were opened to allow other serializers. The main thing is to allow a LegacyHeadersSerializer that can process the old headers from the 2.x store.

[github-actions]

Hello 👋

here is the most recent benchmark result:

SimpleSetupBench
================

+----------------------------------------+--------------------+--------------------+-----------+-----------------+------------+-------------+
|                                        | time (kde mode)                                     | memory                                     |
+----------------------------------------+--------------------+--------------------+-----------+-----------------+------------+-------------+
| subject                                | Tag: <current>     | Tag: base          | time-diff | Tag: <current>  | Tag: base  | memory-diff |
+----------------------------------------+--------------------+--------------------+-----------+-----------------+------------+-------------+
| benchLoad10000Events ()                | 52.722ms (±0.00%)  | 53.541ms (±0.00%)  | -1.53%    | 34.194mb        | 34.202mb   | -0.02%      |
| benchSave1Event ()                     | 978.000μs (±0.00%) | 1.012ms (±0.00%)   | -3.34%    | 34.194mb        | 33.692mb   | +1.49%      |
| benchSave10000Events ()                | 222.555ms (±0.00%) | 234.536ms (±0.00%) | -5.11%    | 33.692mb        | 33.692mb   | 0.00%       |
| benchSave10000Aggregates ()            | 8.695s (±0.00%)    | 8.807s (±0.00%)    | -1.27%    | 33.692mb        | 33.692mb   | 0.00%       |
| benchSave10000AggregatesTransaction () | 6.721s (±0.00%)    | 6.748s (±0.00%)    | -0.40%    | 33.692mb        | 33.692mb   | 0.00%       |
+----------------------------------------+--------------------+--------------------+-----------+-----------------+------------+-------------+

SnapshotsBench
==============

+----------------------------------------+--------------------+--------------------+-----------+-----------------+------------+-------------+
|                                        | time (kde mode)                                     | memory                                     |
+----------------------------------------+--------------------+--------------------+-----------+-----------------+------------+-------------+
| subject                                | Tag: <current>     | Tag: base          | time-diff | Tag: <current>  | Tag: base  | memory-diff |
+----------------------------------------+--------------------+--------------------+-----------+-----------------+------------+-------------+
| benchLoad10000EventsMissingSnapshot () | 54.129ms (±0.00%)  | 54.101ms (±0.00%)  | +0.05%    | 33.763mb        | 33.763mb   | 0.00%       |
| benchLoad10000Events ()                | 824.200μs (±0.00%) | 881.500μs (±0.00%) | -6.50%    | 33.763mb        | 33.763mb   | 0.00%       |
+----------------------------------------+--------------------+--------------------+-----------+-----------------+------------+-------------+

SplitStreamBench
================

+-------------------------+--------------------+--------------------+-----------+-----------------+------------+-------------+
|                         | time (kde mode)                                     | memory                                     |
+-------------------------+--------------------+--------------------+-----------+-----------------+------------+-------------+
| subject                 | Tag: <current>     | Tag: base          | time-diff | Tag: <current>  | Tag: base  | memory-diff |
+-------------------------+--------------------+--------------------+-----------+-----------------+------------+-------------+
| benchLoad10000Events () | 4.967ms (±0.00%)   | 5.049ms (±0.00%)   | -1.61%    | 37.070mb        | 37.070mb   | 0.00%       |
| benchSave10000Events () | 380.317ms (±0.00%) | 394.970ms (±0.00%) | -3.71%    | 37.071mb        | 37.071mb   | 0.00%       |
+-------------------------+--------------------+--------------------+-----------+-----------------+------------+-------------+

SubscriptionEngineBench
=======================

+---------------------------+-----------------+-----------------+-----------+-----------------+------------+-------------+
|                           | time (kde mode)                               | memory                                     |
+---------------------------+-----------------+-----------------+-----------+-----------------+------------+-------------+
| subject                   | Tag: <current>  | Tag: base       | time-diff | Tag: <current>  | Tag: base  | memory-diff |
+---------------------------+-----------------+-----------------+-----------+-----------------+------------+-------------+
| benchHandle10000Events () | 3.014s (±0.00%) | 3.018s (±0.00%) | -0.10%    | 34.161mb        | 34.161mb   | 0.00%       |
+---------------------------+-----------------+-----------------+-----------+-----------------+------------+-------------+

PersonalDataBench
=================

+----------------------------------------+--------------------+--------------------+-----------+-----------------+------------+-------------+
|                                        | time (kde mode)                                     | memory                                     |
+----------------------------------------+--------------------+--------------------+-----------+-----------------+------------+-------------+
| subject                                | Tag: <current>     | Tag: base          | time-diff | Tag: <current>  | Tag: base  | memory-diff |
+----------------------------------------+--------------------+--------------------+-----------+-----------------+------------+-------------+
| benchLoad10000Events ()                | 86.679ms (±0.00%)  | 89.928ms (±0.00%)  | -3.61%    | 35.778mb        | 35.778mb   | 0.00%       |
| benchSave1Event ()                     | 1.569ms (±0.00%)   | 1.443ms (±0.00%)   | +8.73%    | 35.778mb        | 35.778mb   | 0.00%       |
| benchSave10000Events ()                | 253.751ms (±0.00%) | 258.857ms (±0.00%) | -1.97%    | 35.780mb        | 35.780mb   | 0.00%       |
| benchSave10000Aggregates ()            | 12.491s (±0.00%)   | 12.672s (±0.00%)   | -1.43%    | 35.778mb        | 35.778mb   | 0.00%       |
| benchSave10000AggregatesTransaction () | 10.725s (±0.00%)   | 10.742s (±0.00%)   | -0.16%    | 36.280mb        | 36.280mb   | 0.00%       |
+----------------------------------------+--------------------+--------------------+-----------+-----------------+------------+-------------+

This comment gets update everytime a new commit comes in!