feat(tpm): add type-safe NV certify attestation parsing

[noah-ing]

What

Add a shared TPMS_ATTEST dispatch parser and a type-enforcing TPM_ST_ATTEST_NV entry point for TPMS_NV_CERTIFY_INFO.

Why

This addresses the NV-certify consolidation scope added in #255. cMCP currently carries a local parser because parse_tpm_quote() assumes the quote union and rejects TPM_ST_ATTEST_NV. The new API lets consumers inspect the signed common header and safely parse a full NV certify without reimplementing TPM wire offsets.

The high-level parse_tpm_nv_certify() checks the signed attestation type before interpreting the union. The lower-level union parser remains available for callers that already dispatched on TpmAttest.attest_type. Size-prefixed TPM2B_ATTEST input must consume the full outer buffer; undeclared trailing bytes now fail closed.

This is the NV-certify portion of #255 only. It does not claim to close the remaining digest-agility or verification work.

Spec impact

None. SDK-only; no normative or conformance-level change.

Test plan

• pytest -q tests - 874 passed, 6 skipped
• mypy src/agent_manifest passes
• ruff check src tests --select E,F,W --ignore E501 passes
• bandit -r src/agent_manifest -c pyproject.toml passes
• New tests cover bare and TPM2B framing, a non-empty qualified signer, type confusion rejection, truncation, trailing bytes, public exports, and the maximum UINT16 offset
• CHANGELOG.md updated

DCO

All commits in this PR are signed off (git commit -s). By submitting this PR I certify the Developer Certificate of Origin.

[github-actions]

🟡 Contributor Check: MEDIUM

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[imran-siddique]

Reviewed the TPM wire parsing, framing/bounds behavior, public exports, regression coverage, and security-sensitive type separation. The common TPMS_ATTEST header and TPM_ST_ATTEST_NV union layout match the current TCG Part 2 structures; the distinct TPM_ST_ATTEST_NV_DIGEST selector is not conflated. CI evidence is green across lint, typing, security scan, governance, build, and completed test platforms. Approved.