Fix Bifrost same-owner reference benchmark regressions

[DavidBakerEffendi]

Description

Fix the UsageBench/Bifrost contract mismatch introduced when Bifrost began excluding same-owner receiver usages from its default external-usage surface.

UsageBench measures an LSP-shaped reference surface, so the adapter must explicitly request and normalize those references. This restores the eight Go, PHP, Python, and Ruby benchmark cases that regressed when scheduled runs picked up the newer Bifrost master.

Key Changes:

• Request include_same_owner: true from scan_usages_by_location.
• Normalize same_owner_files as proven reference locations for both current and legacy response shapes.
• Add focused request and parser coverage, and document the adapter contract.

Validation:

• cargo fmt --check
• cargo test — 108 tests passed
• cargo run -- validate benchmarks/cases — 35 documents validated
• Full benchmark against Bifrost da37db3 — restored all eight regressed cases, returning to 133 passed / 16 pre-existing failures
• Compatibility probe against prior Bifrost 011ee62 — passed

Touch Points:

• src/runners/bifrost.rs
• docs/runner-adapters.md