Bun parity: complete Windows named-pipe errors, duplicate listen, and node:http reuse

Tracks genuine Windows named-pipe failures from #66: pipe connect errors, duplicate server path listen, and node:http Unix-socket keepalive semantics.\n\nAcceptance criteria:\n- preserve ENOENT, ENOTSOCK, EACCES, EINVAL, EADDRINUSE, EADDRNOTAVAIL, and ECONNRESET from native and libuv failures\n- normalize listen(path), listen({path}), and callback forms\n- report duplicate path EADDRINUSE asynchronously with syscall and path\n- integrate node:http and Agent socketPath with Windows named-pipe listeners\n- reuse one keepalive connection across sequential requests and report getConnections accurately\n- add direct connectable-path and duplicate-listen Windows tests\n\nParent tracker: #66

Implementation is complete locally across 098019730 and b1fcb36 (push queued by github.com DNS failure). The logical corpus layer passes exact copied net-pipe-connect-errors and net-server-listen-path fixtures, plus net-pingpong, with 20 consecutive combined runs (100 focused executions). Native code now preserves libuv error identity, formats duplicate listen errors with syscall/path, cleans synchronous and asynchronous pre-open failures without pipe/context/socket leaks, and supports HTTP socketPath lifecycle plumbing. Keep open for real Windows connectable-path, duplicate-listen, and keepalive validation.