HKDF cached key support

[bigbrett]

Adds (requested) feature to use cached key as input to HKDF. Follow up to #204

Also makes some unrelated keycache input pointers const-correct

[Copilot]

Pull Request Overview

This PR adds support for using cached keys as input key material for HKDF operations, allowing keys already stored in the HSM to be used directly without passing key data from the client. This extends HKDF functionality by distinguishing between input key IDs (keyIdIn) and output key IDs (keyIdOut).

• Introduces keyIdIn parameter to specify cached input key material
• Updates HKDF request/response structures to separate input and output key IDs
• Adds server-side logic to retrieve and use cached keys for HKDF operations

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
wolfhsm/wh_message_crypto.h	Splits keyId field into keyIdIn and keyIdOut in HKDF request/response structures
wolfhsm/wh_client_crypto.h	Updates function signatures to include keyIdIn parameter with documentation
src/wh_message_crypto.c	Updates serialization to handle separate keyIdIn and keyIdOut fields
src/wh_server_crypto.c	Implements cached key retrieval logic for HKDF input key material
src/wh_client_crypto.c	Updates client API implementation to pass keyIdIn parameter
src/wh_client_cryptocb.c	Updates crypto callback to use WH_KEYID_ERASED for keyIdIn parameter
test/wh_test_crypto.c	Adds test case verifying cached input key functionality
examples/demo/client/wh_demo_client_crypto.h	Adds function declaration for new demo
examples/demo/client/wh_demo_client_crypto.c	Implements demo showing cached input key usage
examples/demo/client/wh_demo_client_all.c	Integrates new demo into demo suite

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[billphipps]

Looks good! Consider freshen key instead of read key API.