MEDIUM: SNP report measurement field not compared with expected value — measurement tampering undetected (HW-002) #172

In _hw_providers.py, get_attestation_report() extracts the measurement field from the SNP report but does not compare it against an expected measurement hash. An attacker who replays a valid report for a different binary will pass. Fix: add a expected_measurement parameter to SEVSNPProvider and compare with hmac.compare_digest() at verification time.