net: support sending net.BoundSocket to worker threads and child processes

[guybedford]

This adds support for transferring net.BoundSocket instances to other threads via the worker_threads postMessage() transfer list, and for sending them to child processes as the sendHandle argument of subprocess.send(), following on from #64399 and #64460.

A BoundSocket reserves a port synchronously at construction time. Making it transferable means a port can be reserved on one thread or process and the bound handle handed off to another to listen or connect on, without racing on the bind.

• BoundSocket implements [kTransfer]/[kTransferList]/[kDeserialize], moving the underlying TCP handle with the same mechanism used for net.Socket and net.Server transfer.
• subprocess.send()/process.send() accept a BoundSocket as sendHandle: the handleConversion entry reuses the transfer protocol on the sending side and the _TransferredBoundSocket deserialization path on the receiving side. The transport is the same as cluster's shared-handle scheduling (SCM_RIGHTS on Unix, WSADuplicateSocket on Windows), both of which carry bind state.
• After transfer or send, the source instance behaves as if adopted: address(), fd() and close() throw ERR_SOCKET_HANDLE_ADOPTED.
• Transfer requires an un-adopted, open TCP handle, otherwise ERR_WORKER_HANDLE_NOT_TRANSFERABLE is thrown. Pipe (path) binds are not transferable, and throw ERR_INVALID_HANDLE_TYPE when sent over IPC.
• On the receiving side the local address is re-derived from the handle rather than trusted from serialized state.

Tests cover a parent-to-worker transfer and a parent-to-child-process send where the receiver listens on the transferred bind, plus guard cases (closed, adopted and pipe-bound sockets). Docs updated in net.md, worker_threads.md, child_process.md and errors.md.

[nodejs-github-bot]

Review requested:

• @nodejs/net

[codecov]

Codecov Report

❌ Patch coverage is 91.07143% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.14%. Comparing base (b420cb6) to head (b21b5f1).
⚠️ Report is 24 commits behind head on main.

Files with missing lines	Patch %	Lines
lib/net.js	89.06%	7 Missing ⚠️
lib/internal/child_process.js	93.75%	3 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main   #64725    +/-   ##
========================================
  Coverage   90.13%   90.14%            
========================================
  Files         743      744     +1     
  Lines      242412   242612   +200     
  Branches    45655    45697    +42     
========================================
+ Hits       218510   218693   +183     
- Misses      15403    15418    +15     
- Partials     8499     8501     +2     

Files with missing lines	Coverage Δ
lib/internal/child_process.js	94.87% <93.75%> (+0.13%)	⬆️
lib/net.js	94.50% <89.06%> (+0.07%)	⬆️

... and 36 files with indirect coverage changes

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[mcollina]

lgtm

[guybedford]

I've updated this PR to also include support for transferring a BoundSocket to a child process.