perf(stages): use regular rayon spawn

[mattsse]

the spawn_fifo differs from the regular spawn function:

https://github.com/rayon-rs/rfcs/blob/master/accepted/rfc0001-scope-scheduling.md

spawn_fifo has apparently some additional overhead since there's some syncing involved.

we already sort all the responses so we can just use the regular spawn function

[rkrasiuk]

👀

[codecov-commenter]

Codecov Report

Merging #1832 (ed46de8) into main (661a242) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##             main    #1832      +/-   ##
==========================================
- Coverage   73.50%   73.49%   -0.02%     
==========================================
  Files         410      410              
  Lines       50510    50515       +5     
==========================================
- Hits        37129    37127       -2     
- Misses      13381    13388       +7     

Flag	Coverage Δ
integration-tests	19.73% <0.00%> (+0.02%)	⬆️
unit-tests	67.84% <100.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
crates/stages/src/stages/sender_recovery.rs	91.19% <100.00%> (-0.30%)	⬇️

... and 5 files with indirect coverage changes

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