Activate full Bun.serve HTTP/3 UDP corpus

Scope\n\nActivate the complete byte-identical upstream js/bun/http/serve-http3.test.ts corpus in Home instead of rewriting the whole file to one TODO.\n\nCurrent baseline:\n- 0 passed\n- 0 failed\n- 0 unsupported\n- 1 TODO\n- 45 original tests\n- Home/upstream SHA-256: 6813da0085970f937629472d146c1380cf4b54b96939b34cffaa6d9d1de60683\n\nRequired behavior:\n- true HTTP/3-tagged HTTPS fetch routing with UDP-only versus dual HTTP/1.1 behavior\n- http3/tls/http1/unix validation\n- dynamic and static routes, params, method fallthrough, files, ranges, HEAD and Alt-Svc\n- streamed, passthrough, subprocess, 512 KiB, 2 MiB, and 8 MiB response/request bodies\n- 64 concurrent streams and cross-stream body isolation\n- client abort/RST and request AbortSignal handling\n- maxRequestBodySize without Content-Length\n- request metadata lifetime and requestIP\n- server.url/address, reload, abrupt stop, graceful drain, natural exit and closed-listener rejection\n- H3 server.upgrade returns false without crashing\n- preserve the upstream corpus unchanged\n- add a durable exact-corpus regression and pass the complete Home gate\n\nThis follows #179 and remains tracked under #66.

Completed on main in 01ae1bd.

Verification:

• Source fidelity: Home and ~/Code/bun copies of serve-http3.test.ts are byte-identical at SHA-256 6813da0085970f937629472d146c1380cf4b54b96939b34cffaa6d9d1de60683.
• Exact untouched corpus: 45 passed, 0 failed, 0 TODO, 0 unsupported.
• Coverage includes UDP-only and dual-transport validation; routes, params, and method fallthrough; ETag, ranges, HEAD, and files; 512 KiB, 2 MiB, and 8 MiB bodies; 64 streams; transformed-body isolation; abort/RST/request-signal propagation; reload; abrupt/graceful stop and natural exit; request lifetime/requestIP; Alt-Svc; and upgrade: false.
• Home now supplies protocol-tagged long-lived servers, commandable lifecycle handling, push-driven stderr, fixture routes and bodies, dual-stack checks, and zero-active-request accounting.
• Exact activation exposed and fixed two shared runtime defects: stream-producer re-entry duplicated response chunks, and client aborts were not propagated onto the server-side Request.signal.
• Adjacent fast corpus: 287 active passes, with 2 explicit upstream TODOs.
• Body-leak stress: 7/7 passed, all scenarios at leak 0, stable RSS start/peak/end of 67,108,864 bytes, retaining the original 140,000 POST cycles.
• Full home_test gate: 1,138 passed, 1 skipped, 0 failed (1,139 total); exit 0 in 1,384.15s.