🛠️ Refactor: Fix linters errors and reduce allocations

[google-labs-jules]

This PR addresses a few code quality issues and static analysis warnings:

• Replaced ineffective break statement with return nil in tcp.go to correctly break out of the loop and function, fixing SA4011.
• Updated sync.Pool usage to store and return *[]byte instead of []byte in tcp.go to avoid interface boxing overhead and allocations, fixing SA6002.
• Added explicit error handling and suppression for ln.Close(), c1.Close(), dst.Close(), src.Close(), and server.Serve(ln) in proxy.go and tcp.go to satisfy linter checks.

Assumptions

• Implicitly ignoring shutdown errors via _ = on Close() calls is acceptable since we cannot realistically recover from them during server shutdown or connection dropping.

Alternatives Not Chosen

• Continuing to use a break with a loop label instead of return nil for the SA4011 fix. return nil is simpler and correctly stops serving when the context is cancelled.

How To Pivot

• If explicitly returning from the loop is undesirable, you can wrap the loop in a label serveLoop: and replace return nil with break serveLoop.
• If tracking errors in Close() methods is necessary, you can log them using slog.Error instead of using _ =.

Next Knobs

• The bufferPool size is still fixed to 1<<15. This could be made configurable via flags or TailscaleProxyServerOptions.

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PR created automatically by Jules for task 9962427522576436097 started by @lucasew

[google-labs-jules]

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