fix: stop buffering data after SOCKS5 connect

[trivikr]

This relates to...

Fixes: #5117

Rationale

After a SOCKS5 CONNECT succeeds, the socket carries tunneled HTTP/TLS data and should no longer be parsed by Socks5Client. The existing permanent data listener kept appending tunneled response chunks to the internal protocol buffer, causing duplicate retained memory for the lifetime of the socket.

Changes

• Store the SOCKS5 socket data handler so it can be removed after CONNECT succeeds.
• Clear the SOCKS5 protocol buffer once the CONNECT response is parsed.
• Preserve any tunneled bytes that arrive in the same socket read as the CONNECT response by pushing them back with socket.unshift().

Features

N/A

Bug Fixes

Stop buffering data after SOCKS5 connect

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 93.14%. Comparing base (efae3da) to head (f8a876f).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5118      +/-   ##
==========================================
- Coverage   93.14%   93.14%   -0.01%     
==========================================
  Files         110      110              
  Lines       35908    36109     +201     
==========================================
+ Hits        33446    33633     +187     
- Misses       2462     2476      +14     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[mcollina]

Does this need to be reallocated? We could just keep one around, they are just empty.

[trivikr]

The SOCKS5 client removes its data listener, but the client object can still be retained by the socket’s error/close listeners. If this.buffer is not cleared, it can retain the SOCKS5 response buffer.

We don't need fresh allocation every time, as it's replaced using Buffer.concat(...)
I replaced this with EMPTY_BUFFER constant in f8a876f

[mcollina]

lgtm