[Rhythm] Block-builder improvement to skip WAL

[mdisibio]

What this PR does:
Update the block-builder to skip the WAL and go directly from in-memory live traces to the backend block. This is more efficient and the block-builders have much higher throughput. Memory allocs are improved, but total working must now be large enough to contain the full cycle of data. Overall the higher throughput is the most important for operational reasons.

               │ before.txt  │              after.txt              │
               │   sec/op    │   sec/op     vs base                │
BlockBuilder-4   808.0m ± 1%   374.7m ± 2%  -53.63% (p=0.000 n=10)

               │  before.txt  │               after.txt               │
               │     B/s      │     B/s       vs base                 │
BlockBuilder-4   36.17Mi ± 1%   78.41Mi ± 1%  +116.80% (p=0.000 n=10)

               │  before.txt   │              after.txt               │
               │     B/op      │     B/op      vs base                │
BlockBuilder-4   1165.5Mi ± 2%   839.9Mi ± 2%  -27.94% (p=0.000 n=10)

               │ before.txt  │             after.txt              │
               │  allocs/op  │  allocs/op   vs base               │
BlockBuilder-4   5.773M ± 0%   5.417M ± 0%  -6.17% (p=0.000 n=10)

Which issue(s) this PR fixes:
Fixes #

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]