coro: integrate LLVM 22 runtime fast paths

[cpunion]

Integrates the current LLVM 22-only correctness and performance series into llvm-coro.

Highlights:

• preserve heap lifetime and preemption across physical coroutine calls
• collapse static interface, scheduler handoff, completion, and inline-await validation
• fuse the compiler-owned single-worker park transaction while retaining generic cancellation/select fallbacks
• keep regular files on the bounded worker source and sockets on the nonblocking poll path
• keep all WebAssembly IR consumers on LLVM 22
• make compiler-rt freestanding WASM builds independent of host libc headers
• close source-island and cgo C2 static-errno-itab validation gaps

Validation:

• full runtime go test -count=1 ./...
• runtime race tests
• broad compiler coroutine suite
• exact native and JS/WASM keyed-registry source-island gates
• actual standard-library file, TCP, time/timer/sync, WASI, wasip2, and wasm-unknown acceptance through CI
• LLVM 22.1.8 -O3 -lto=full build plus file 10,000 and TCP 5,000 stress runs

Same-host 21-run medians versus the PR parent artifact (500 operations):

• file: 10.309 ms -> 9.071 ms
• TCP: 22.214 ms -> 19.711 ms

The isolated worker-park change improves file median by about 9% and leaves TCP neutral; the stripped workload artifact is 7,666,544 bytes.