fix: destroy socket on SOCKS5 negotiation timeout

[mcollina]

Fixes #5704

Socks5ProxyAgent's createSocks5Connection() rejected its promises on the SOCKS5 auth and CONNECT negotiation timeouts without destroying the underlying socket. Because the socket is never handed to the per-origin Pool (the connect callback that would register it is never reached), it's completely untracked — agent.close()/agent.destroy() only iterate this[kPools], so neither can reach it. A proxy that accepts the TCP connection but stalls during negotiation leaks one open socket per attempt for the lifetime of the process.

This calls socks5Client.destroy() in both timeout paths before rejecting, tearing down the socket (matching the cleanup already done on the error path).

A regression test spins up a proxy that accepts the connection, drains the SOCKS5 greeting, but never replies, then verifies the proxy-side socket is destroyed after the request rejects and agent.close() resolves.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 93.47%. Comparing base (dd85997) to head (db85942).
⚠️ Report is 15 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/dispatcher/socks5-proxy-agent.js	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5706      +/-   ##
==========================================
+ Coverage   93.43%   93.47%   +0.03%     
==========================================
  Files         110      110              
  Lines       38733    38894     +161     
==========================================
+ Hits        36190    36355     +165     
+ Misses       2543     2539       -4     

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