Add TCP connection and listener tracking maps

[sirzooro]

New data structures for managing TCP state inside vnet, plus the minimal type stubs they depend on.

• TCPConn: bare-minimum struct implementing transport.TCPConn; holds locAddr/remAddr and exposes LocalAddr()/RemoteAddr(). All other methods return transport.ErrNotSupported.
• TCPListener: bare-minimum struct implementing transport.TCPListener; holds locAddr and exposes Addr(). All other methods return transport.ErrNotSupported.
• tcpConnMap: thread-safe map of active TCP connections keyed by 4-tuple, with insert, findByChunk, deleteConn, deleteByAddr, and portInUse helpers.
• tcpListenerMap: thread-safe map of TCP listeners keyed by local address, with insert, find, and delete helpers.
• Full unit tests for both maps.

Split out from #375

[codecov]

Codecov Report

❌ Patch coverage is 75.40984% with 45 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.08%. Comparing base (55e2272) to head (766cdb0).

Files with missing lines	Patch %	Lines
vnet/tcp_conn.go	11.76%	30 Missing ⚠️
vnet/tcp_listener.go	20.00%	8 Missing ⚠️
vnet/tcp_map.go	94.96%	3 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #389      +/-   ##
==========================================
- Coverage   84.62%   84.08%   -0.54%     
==========================================
  Files          38       41       +3     
  Lines        3173     3356     +183     
==========================================
+ Hits         2685     2822     +137     
- Misses        355      395      +40     
- Partials      133      139       +6     

Flag	Coverage Δ
go	84.08% <75.40%> (-0.54%)	⬇️

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[Copilot]

Pull request overview

This PR introduces initial TCP state-tracking primitives for vnet: minimal transport.TCPConn/transport.TCPListener stub types plus thread-safe maps to register, look up, and delete TCP listeners and active connections, along with unit tests to validate core behaviors.

Changes:

• Added TCPConn and TCPListener stub implementations that expose addresses and otherwise return transport.ErrNotSupported.
• Added tcpConnMap and tcpListenerMap for tracking TCP connections/listeners by address/tuple with concurrency protection.
• Added unit tests covering insertion, lookup, deletion, and port-in-use checks.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 5 comments.

File	Description
vnet/tcp_map.go	Introduces TCP listener/connection tracking maps and lookup/delete helpers.
vnet/tcp_map_test.go	Adds unit tests validating tcpListenerMap and tcpConnMap behaviors.
vnet/tcp_listener.go	Adds minimal transport.TCPListener stub for vnet.
vnet/tcp_conn.go	Adds minimal transport.TCPConn stub for vnet.

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[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

[sirzooro]

Thanks!