IOCP: accepted pipes on the loop's own port take the thread-pool bridge on every I/O #9

Accepted named pipes are always marked routed = true (backend/iocp/mod.rs, Accept for PipeListener), even when they stay associated with this loop's own completion port.

Every read and write on them then costs:

• a RegisterWaitForSingleObject (heap-allocated inside ntdll),
• a thread-pool hop,
• a blocking UnregisterWaitEx.

This is the Node IPC path. ipc_handle_transfer_and_external_waits_allocate_nothing_after_setup still passes only because the Rust counting allocator can't see ntdll's heap, so DESIGN §10 rule 1 holds only nominally.

Expected:

• Skip the bridge when the handle's association is this loop's own port.
• Add a Windows test that proves an accepted pipe on the same loop does no wait registration, for example via a debug counter of bridge registrations.

Found in the PR #5 integrator review (item 6).