Add mock-based coverage for session reuse, reconnect behavior,

[shadrach68]

• closes Improve session persistence for HSM signing and PKCS11 #329

Summary
This PR improves PKCS#11/HSM audit signing by making session handling more robust and predictable. The signer now reuses initialized PKCS#11 sessions and cached key lookups across signing operations, retries once when a cached session becomes stale, and returns clearer validation and runtime error messages for common failure cases.

Changes

• Persist PKCS#11 module/session/key state for the lifetime of the signer
• Retry once after stale session errors such as invalid or closed handles
• Validate invalid PKCS#11 inputs earlier, including slot, algorithm, key ID, and public key PEM
• Improve diagnostics for module load, token selection, login, key lookup, and signing failures
• Add signer cleanup support and command-side cleanup handling
• Expand PKCS#11 mocks and tests to cover session reuse, reconnect behavior, and new validation paths
• Update README guidance for persistent PKCS#11 session behavior and public key configuration

Validation

• npm exec -- jest --runInBand tests/pkcs11Signer.test.ts tests/pkcs11Signer.signing.test.ts src/commands/__tests__/audit.sign.spec.ts

All 27 focused tests passed.

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