lib: fix benchmark record acknowledgement race

[panva]

The child can receive an acknowledgement and send its next record before the parent's send callback runs. Clear recordPending before sending the acknowledgement to avoid rejecting that record as an invalid sequence.

Add a regression test that delays send callbacks until the child sends its next record or closes.

https://ci.nodejs.org/job/node-test-binary-windows-js-suites/43703/RUN_SUBSET=0,nodes=win2022-COMPILED_BY-vs2022_clang/testReport/junit/(root)/parallel/test_bench_cli_backpressure/

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.39%. Comparing base (cede7e6) to head (1becba6).

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #66430   +/-   ##
=======================================
  Coverage   90.39%   90.39%           
=======================================
  Files         792      792           
  Lines      275697   275698    +1     
  Branches    52868    52854   -14     
=======================================
+ Hits       249208   249213    +5     
- Misses      16892    16896    +4     
+ Partials     9597     9589    -8     

Files with missing lines	Coverage Δ
lib/internal/bench_runner/cli.js	94.15% <100.00%> (+<0.01%)	⬆️

... and 36 files with indirect coverage changes

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