fix: select fd_set ABI, poll busy-loop, vdiag switch, condvar lock

[Bahtya]

Summary

• fix: select() fd_set missing bounds check for fd >= FD_SETSIZE #31 CRITICAL: Replace incorrect u32[32] fd_set casts with libc::FD_ISSET/libc::FD_SET (correct u64[16] on aarch64). Add fd >= FD_SETSIZE bounds check. Add compile-time size_of::<fd_set>() == 128 assertion.
• fix: poll() infinite timeout busy-loop when no fds ready #32 HIGH: Fix poll(timeout=-1) infinite busy-loop. IoWait now stores deadline: Option<Instant>, yield_for_io accepts timeout, wake_io_ready expires timed-out coroutines.
• cleanup: excessive vdiag! diagnostic calls in production code #34 MEDIUM: vdiag! macro gated by VPROC_DIAG env var via AtomicBool. Zero write() syscalls when unset (was 68 per ELF load).
• refactor: replace spin-lock in create_process with condvar #36 MEDIUM: Replace 1000×10ms usleep spin-lock in JNI createSubprocess with pthread_cond_timedwait (500ms deadline).

Deferred: #33 (wake_io_ready O(n²) — negligible at 20-50 coroutines), #35 (real_fn macro — pure refactor, 78 call sites, bundle later).

Test plan

• cargo test — all pass
• cargo clippy — 0 warnings
• APK end-to-end — 31/31 pass, hermux round-trip 1028→1017ms (-11ms)
• Cortex-A710/A715/X3 device (MTE enabled) — no crash

Closes #31, closes #32, closes #34, closes #36.

Bahtya