fix: clean up benchmark resources before worker exit

[trivikr]

This relates to...

Fixes: #5213

Rationale

cronometro runs each benchmark case in a worker. Since benchmark.js creates HTTP agents and Undici dispatchers at module scope, each worker can exit with live keep-alive resources. Explicitly cleaning those resources up before worker exit should avoid intermittent native teardown crashes during benchmark runs.

Changes

• Destroy benchmark HTTP agents and Undici dispatchers during cleanup.
• Attach cleanup as a cronometro after hook for each benchmark worker.
• Keep final cleanup after benchmark results are printed.

Features

N/A

Bug Fixes

N/A

Breaking Changes and Deprecations

N/A

Status

• I have read and agreed to the Developer's Certificate of Origin
• Tested
• Benchmarked (optional)
• Documented
• Review ready
• In review
• Merge ready

Assisted-by: openai:gpt-5.5

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.27%. Comparing base (da0eebc) to head (3e029f4).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5225   +/-   ##
=======================================
  Coverage   93.27%   93.27%           
=======================================
  Files         110      110           
  Lines       36353    36353           
=======================================
+ Hits        33907    33909    +2     
+ Misses       2446     2444    -2     

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[mcollina]

lgtm