Quote verification requires the native TPM stack, so it only builds on Linux #95

The verifier feature enables tpm and with it tss-esapi, whose tpm2-tss
FFI bindings only build on Linux. So verifying a vTPM quote — pure computation
over bytes — can't be done from e.g. macOS operator machines or non-Linux
services.

The only tss-esapi use on the verify path is Attest::unmarshall, called in
Quote::verify_pcrs and Quote::nonce to extract two fields (extraData,
pcrDigest) from the marshalled TPMS_ATTEST — a flat big-endian structure
frozen by the TPM 2.0 spec (Part 2 §10.12) that can be parsed in ~100 lines of
dependency-free Rust.

Proposal: parse TPMS_ATTEST in pure Rust and decouple verifier from tpm,
so verification builds and runs on any platform.