Update NATS to 2.10.20, use SyncAlways

[neilalexander]

The internal NATS instance is definitely convenient but it does have one problem: its lifecycle is tied to the Dendrite process. That means if Dendrite panics or OOMs, it takes out NATS with it. I suspect this is sometimes contributing to what people see with stuck streams, as some operations or state might not be written to disk fully before it gets interrupted.

Using SyncAlways means that NATS will effectively use O_SYNC and block writes on flushes, which should improve resiliency against this kind of failure considerably. It might affect performance a little but shouldn't be significant.

Also updates NATS to 2.10.20 as there have been all sorts of fixes since 2.10.7, including better SyncAlways handling.

Signed-off-by: Neil Alexander git@neilalexander.dev

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.19%. Comparing base (7a4ef24) to head (2459fd2).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3418      +/-   ##
==========================================
- Coverage   68.20%   68.19%   -0.01%     
==========================================
  Files         513      513              
  Lines       47021    47022       +1     
==========================================
- Hits        32070    32067       -3     
- Misses      10952    10960       +8     
+ Partials     3999     3995       -4     

Flag	Coverage Δ
unittests	53.31% <100.00%> (+<0.01%)	⬆️

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[S7evinK]

Thanks!