fix(socks5): evict unused origin pools

[Kkartik14]

Fixes #5594

Rationale

Socks5ProxyAgent kept an empty per-origin pool in its internal cache after a SOCKS connection error or a normal target disconnect. A long-lived agent handling many destinations could therefore retain pools indefinitely.

Changes

• remove an idle, non-busy origin pool on connectionError and disconnect
• cover both lifecycle paths with SOCKS5 integration tests

Features

N/A

Bug Fixes

• release unused SOCKS5 origin pools

Breaking Changes and Deprecations

N/A

Status

• I have read and agreed to the Developer's Certificate of Origin
• Tested (test/socks5-proxy-agent.js)
• Benchmarked (optional)
• Documented (not applicable)
• Review ready
• In review
• Merge ready

[mcollina]

lgtm

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.48%. Comparing base (21a8e1e) to head (cff0ad2).
⚠️ Report is 10 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5595   +/-   ##
=======================================
  Coverage   93.47%   93.48%           
=======================================
  Files         110      110           
  Lines       38238    38252   +14     
=======================================
+ Hits        35744    35759   +15     
+ Misses       2494     2493    -1     

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