chore: tweak parameters for seqdb benchmarks

[dkharms]

Description

I've tweaked some parameters to have saturate CPU utilization (now we almost always use 99%-100% of available CPUs).

I'll bring benchmarks results on my machine to demonstrate better performance.

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.26%. Comparing base (627de89) to head (d4d1964).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #162      +/-   ##
==========================================
- Coverage   71.29%   71.26%   -0.03%     
==========================================
  Files         200      200              
  Lines       14557    14557              
==========================================
- Hits        10378    10374       -4     
- Misses       3450     3452       +2     
- Partials      729      731       +2     

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[cheb0]

I checked it. Looks fine, even though it didn't reach full CPU utilization on my machine unless fsync is turned off.