Wire accepted RequestUpdate to the orchestrator's UpdateRequest event

[chrysh]

What

The PLDM firmware-device loop (run_terminus) now notifies an FdEventSink with FdEvent::UpdateRequested once per accepted RequestUpdate, and a new orchestrator-pldm-adapter crate maps that notification to Event::UpdateRequest for the orchestrator. Only RequestUpdate is wired; cancel/completion edges and the run-loop composition are untouched seams.

How

• The seam is a #[non_exhaustive] FdEvent enum plus a single FdEventSink::notify method, so the coming FD lifecycle events (cancel, transfer/verify/apply complete, activate) are one new variant each instead of a trait break for every implementor.
• Every FdEvent payload is Copy and lifetime-free by design. Across the DSP0267 FD surface the orchestrator-relevant edges carry only small integers (result codes, component ids, bitmaps); buffer-shaped data (image chunks, package data, version strings) lands behind FdOps and events name it instead of carrying it.
• The accepted RequestUpdate is detected as the FD's only Idle → non-Idle transition, sampled around the responder poll, after the success response is sent. Rejected requests (ALREADY_IN_UPDATE_MODE, bad transfer size) leave the state unchanged and never notify.
• The sink trait stays PLDM-flavored so the service crate never depends on the orchestrator stack. The mapping lives in services/orchestrator/adapters/pldm as UpdateRequestLatch, following the same rule that keeps HAL adapters out of orchestrator-capabilities. The latch matches UpdateRequested and drops unmapped variants.
• The latch is a bool, not a counter: the FD rejects a second RequestUpdate while one is in progress, and an undrained latch across update cycles coalesces into the single UpdateRequest the state machine would act on anyway.

Tests

• firmware_update_host drives the latch end to end: the accepted RequestUpdate latches exactly one Event::UpdateRequest, a duplicate is rejected with AlreadyInUpdateMode and latches nothing, and no later command in the flow latches anything.
• The adapter crate tests latch semantics (empty, exactly-once, coalescing).