chore: minor performance improvements in bitswap

[gammazero]

Reduce lock contention, gc load, and other minor performance improvements.

[codecov]

Codecov Report

Attention: Patch coverage is 93.87755% with 3 lines in your changes missing coverage. Please review.

Project coverage is 60.24%. Comparing base (317eb7d) to head (f4c485f).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...swap/server/internal/decision/blockstoremanager.go	93.61%	2 Missing and 1 partial ⚠️

@@            Coverage Diff             @@
##             main     #666      +/-   ##
==========================================
+ Coverage   60.20%   60.24%   +0.03%     
==========================================
  Files         241      241              
  Lines       30681    30707      +26     
==========================================
+ Hits        18473    18498      +25     
  Misses      10560    10560              
- Partials     1648     1649       +1     

Files with missing lines	Coverage Δ
bitswap/server/internal/decision/engine.go	91.78% <100.00%> (-0.06%)	⬇️
...swap/server/internal/decision/blockstoremanager.go	90.75% <93.61%> (-0.26%)	⬇️

... and 16 files with indirect coverage changes

[lidel]

ps. congrats on PR number 😈