feat(parse): support route-views sh ip bgp snapshots

[digizeph]

Summary

Adds support for route-views sh ip bgp snapshots (e.g. oix-full-snapshot-2026-07-01-0000.bz2) to monocle parse. Closes #145.

Route-views dumps use the same fixed-width column layout as PCH Cisco dumps but omit the BGP table version / local AS preamble and use a different filename timestamp format.

Changes

• Detection: detect_text_dump also matches dumps opening with Status codes: (route-views dumps have no BGP table line, and Next Hop sits beyond the 128-byte sniff window).
• Missing preamble tolerated: when router ID / local AS are absent, peer_ip / peer_asn default to the unspecified sentinels 0.0.0.0 and AS0 instead of erroring out. The fixed-width column parsing itself is unchanged — it already derives positions from the column header, so the 3-space-indent route-views layout parses as-is.
• Timestamp inference: infer_timestamp_from_path now recognizes YYYY-MM-DD-HHMM (route-views snapshot filenames) and uses the embedded time of day. PCH-style YYYY.MM.DD (noon UTC) behavior is unchanged.

Testing

• New unit tests: route-views detection, full route-views-style dump parse (sentinel peer values, MED/path/origin extraction), route-views + PCH timestamp inference, no-date fallback.
• Real-data check on oix-full-snapshot-2026-07-01-0000 (first 200k lines): 78,976/78,976 route lines parsed, timestamp inferred as 1782864000 (2026-07-01 00:00 UTC) from the filename.
• MRT export round-trip works; MrtRibEncoder collapses multiple paths per (peer, prefix) into one RIB entry, so a multi-peer-flattened oix dump exports as 5,336 unique prefixes — expected for a single-peer TABLE_DUMP_V2 encoding.
• cargo fmt --check, cargo clippy --all-features -- -D warnings, and cargo test --all-features (318 tests) all pass.