[Async] Add primitive handle dup/close and tests

Add iree_async_primitive_dup() and iree_async_primitive_close() for
cross-process handle transfer. These are the async primitive layer's
equivalents of dup()/close() (POSIX), DuplicateHandle/CloseHandle
(Windows), and mach_port_mod_refs/deallocate (macOS).

Needed by the SHM handshake to duplicate shared_wake signal primitives
for IPC exchange, and by the factory to dup accepted socket primitives
before passing them to the handshake (which takes ownership).

Also adds primitive_test covering construction helpers (none, is_none,
make, from_fd, from_win32_handle, from_mach_port), dup semantics
(NONE fails, produces independent handle, multiple dups independent),
and close semantics (NONE/NULL noop, sets to NONE).

Co-Authored-By: Claude <noreply@anthropic.com>