feat(fw): implement DDI DeleteKey handler

[jaygmsft]

Wire up the previously-unimplemented DeleteKey (1014) DDI op in the firmware application layer: within an open session, delete a vault-resident key by id and return an empty success response.

• Internal device keys (anything carrying the internal attribute — the partition unwrapping key, session and credential keys) cannot be destroyed by the host and are rejected with CannotDeleteInternalKeys, matching the reference firmware.
• An unknown key_id is rejected with KeyNotFound.
• Session validation is framework-level (DeleteKey -> InSession), so a missing/mismatched session returns FileHandleSessionIdDoesNotMatch.

The handler is synchronous: the internal-attribute check and the vault deletion have no yield point between them, so no partition_lock is needed.

New: delete_key.rs handler; mod.rs dispatch wiring; delete_key_smoke.rs smoke tests (delete + reuse, unknown-key, and double-delete idempotency using an app AES key, so they run on both backends).

Validation:

• emu delete_key_smoke 3/3; mock 3/3.
• mock delete_key integration 8/8 (includes CannotDeleteInternalKeys for the unwrapping key). On emu the core delete_key integration tests pass (6/8); the unwrapping-key and bulk-import cases are setup-blocked by GetUnwrappingKey / RsaUnwrap, which are not yet implemented on main (a pre-existing limitation, not this handler) — the internal-key path is exercised on mock instead.
• emu smoke 33/33 (no regression).
• cargo xtask clippy clean; clippy --tests clean under emu and mock; fmt and copyright clean.

[Copilot]

Pull request overview

This PR implements the MBOR DDI DeleteKey (op 1014) firmware handler, wiring it into the firmware dispatcher and adding end-to-end smoke tests to validate delete behavior across both mock and emu backends.

Changes:

• Added a new synchronous firmware handler to delete a vault-resident key by id, rejecting internal keys and unknown ids with the expected DDI statuses.
• Wired DeleteKey into the MBOR module exports and dispatch table.
• Added integration smoke tests covering delete+reuse, unknown key deletion, and double-delete behavior; registered the new test module.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
fw/core/lib/src/ddi/mbor/mod.rs	Exposes the new handler and routes DdiOp::DeleteKey to it in the dispatcher.
fw/core/lib/src/ddi/mbor/delete_key.rs	Implements the firmware-side DeleteKey operation (internal-key rejection, vault delete, empty success response).
ddi/mbor/types/tests/integration/delete_key_smoke.rs	Adds backend-agnostic smoke tests for delete semantics using an app AES key.
ddi/mbor/types/tests/azihsm_ddi_tests.rs	Registers the new delete_key_smoke integration test module.