pkg/storage: Remove storing cumulative values

[metalmatze]

Instead of storing cumulative values, we are going to only store the flat values (these are the values that the leaves have), and then when generating the flame graph we'll calculate the cumulative values on the fly.

This will mostly show in heap usage over time:

Benchmarks for appending got faster and more lightweight as well as querying (although we calculate all cumulative values).

Appends:

name        old time/op    new time/op    delta
Appends-24    16.5ms ± 1%    12.5ms ± 3%   ~     (p=0.100 n=3+3)

name        old alloc/op   new alloc/op   delta
Appends-24    7.24MB ± 0%    6.26MB ± 0%   ~     (p=0.100 n=3+3)

name        old allocs/op  new allocs/op  delta
Appends-24      152k ± 0%      122k ± 0%   ~     (p=0.100 n=3+3)

Iterator:

name         old time/op    new time/op    delta
Iterator-24     144µs ± 1%     104µs ± 5%   ~     (p=0.100 n=3+3)

name         old alloc/op   new alloc/op   delta
Iterator-24    28.7kB ± 0%    28.0kB ± 0%   ~     (p=0.100 n=3+3)

name         old allocs/op  new allocs/op  delta
Iterator-24     1.71k ± 0%     1.70k ± 0%   ~     (p=0.100 n=3+3)

[kakkoyun]

Why comment, not remove?

[metalmatze]

I went through all of these comments and removed them. Seems like I missed a few.
Thanks!

[kakkoyun]

ditto.

[brancz]

I love that we can show here that pre-computing the values actually made things slower. Architecturally looks good, and our regression tests should have caught any inconsistencies in results, so I feel confident that this works as expected!

I don't feel too strongly about the commented-out parts being removed in this or a follow-up PR. Your call.

[metalmatze]

Awesome. Yeah, it's probably to go with this now and do the cleanup in a follow-up. :)
Thanks for the reviews!