tls_context() now defaults to real certificate verification instead of the
tool's original always-CERT_NONE posture; measure_tls() only falls back to
unverified on ssl.SSLCertVerificationError, retiming the retry since the
failed attempt's duration isn't representative. This is also the only way
to get subject/issuer/notAfter at all - getpeercert() returns {} for a
chain that never validated.
Every TLS result now carries cert_sha256 (SHA-256 of the full DER cert, not
the SPKI - that would need the cryptography package, a dependency this
doesn't need), cert_issuer, cert_days_remaining, and the long-dead
cert_verified field finally gets written. New tls.pinned_fingerprints
config (host -> expected hash, capped and hex-validated) drives three new
findings: a pin mismatch is crit, an unpinned validation failure is warn,
an expiring cert is warn.
Live-tested with --tls against real Cloudflare/Google endpoints - verified
handshake, correct issuer and expiry both times.
Part of plans/zesty-zooming-wilkinson.md (gitignored).
