Update Bifrost benchmark expectations

[DavidBakerEffendi]

Description

Update the scheduled Bifrost benchmark expectations after run 34568436261. The change retires seven stale failures while preserving the frozen real-project-v2 source-review contract for newly returned Rust Self references.

Key Changes:

• Retire four C++ overlays, the Rust baseline overlay, and the Scala overlay; promote the authored C# expected failure through the expected-pass overlay.
• Record the three real-project-v2 Rust Self result differences as expected failures without rewriting hash-bound ground truth.
• Expand the overlay regression test to cover the newly referenced Rust case documents.

Touch Points:

• benchmarks/expectations/bifrost-expected-failures.yaml
• benchmarks/expectations/bifrost-expected-passes.yaml
• src/runners/bifrost.rs