perf(rendering): combine caption active and fade lookup

[KrishCodesw]

Summary

• Combine the active-caption and exit-animation lookup loops into one pass.
• Preserve active-caption priority and the first matching exit-animation segment in input order.
• Add regression tests for overlapping and unsorted segments, exact boundaries, and a differential comparison with the previous two-pass implementation.
• Add an ignored release-mode microbenchmark for active, fading, gap, and after-track lookups.

Closes #2523.

Benchmark

The benchmark is included but has not been run in this environment: Rust/Cargo is not installed, and the container cannot reach GitHub to clone the repository. I have not recorded or claimed a performance gain.

Run from the repository root:

cargo test -p cap-rendering benchmark_caption_lookup_before_and_after --release -- --ignored --nocapture

The output compares median lookup time for the original two-pass implementation and the new implementation across 2,400 caption segments. Please keep this PR as a draft until the results confirm a useful gain and no unacceptable regression for active-caption lookups.

Validation

• Added a differential test over overlapping, unsorted segments and multiple fade overrides.
• Added explicit tests for active-over-fading priority, input order, and active/fade boundaries.
• Rust tests and benchmark execution remain unverified in this environment.

Confidence Score: 5/5

No blocking code issues remain; keep the PR draft until the benchmark meets the author's stated release condition.

Summary

Combines active-caption and fade lookup into one pass while preserving selection order.

• Caption rendering checks active and fading segments in one scan.

_{Reviews (2) · Last reviewed commit: "style(rendering): apply rustfmt to capti..." · Reviewed by Greptile}

[vercel]

@KrishCodesw is attempting to deploy a commit to the Cap Software Inc Team on Vercel.

A member of the Team first needs to authorize it.

[richiemcilroy]

Thanks for the PR. Greptile currently has this at 4/5, and we only merge PRs once Greptile scores the current head 5/5. Please address the remaining Greptile feedback, then comment @greptileai to request a re-review, and repeat until it reaches 5/5.

[KrishCodesw]

@greptileai Please re-review the current PR head and update the score. The redundant test comment is absent from the current source, and the Rust formatting changes are committed in 65f56c3.

[KrishCodesw]

@richiemcilroy Thanks! Greptile now scores the latest PR head 5/5. I've addressed the review feedback. Let me know if anything else is needed.

[KrishCodesw]

Hey @richiemcilroy , just wanted to follow up on this PR and check if there are any updates.
Thanks!