feat: RFC 9990 generator/pass-disposition + RFC 9989 obsolete-tag cleanup

[thegushi]

Summary

• report_metadata now includes , identifying the report-generating software, matching the string already used for --version output and the X-Mailer header.
• opendmarc-reports strips the obsolete "!NNNk" RUA size-suffix (obs-dmarc-report-size) from destination addresses but no longer enforces it as a per-destination size cap, per RFC 9989's ABNF ("reporters should ignore" it).
• Removed rf=/ri= parsing, the now-dead DMARC_POLICY_T fields, and the orphaned (never publicly declared) opendmarc_policy_fetch_rf() -- both tags were removed from the DMARC record format by RFC 9989.
• ActionDispositionType now emits "pass" (RFC 9990 S3.1.1.9) alongside none/quarantine/reject: new DMARC_RESULT_PASS is set when alignment passed under an enforcing (reject/quarantine) policy, keyed off the unadjusted published p/sp so t=y step-down doesn't affect it, per the existing rule that t= doesn't affect report generation.

Test plan

• Clean autoreconf && ./configure && make on quark (FreeBSD): no compiler warnings.
• make check: libopendmarc test suite 10/10 pass, including test_dmarc_parse's negative rf=/ri= cases updated to expect DMARC_PARSE_OKAY now that they're unknown (ignored) tags rather than validated ones.
• reports/opendmarc-reports syntax-checked clean with real Perl on quark.