refactor: optimize getExternalProps with for-in loop and startsWith

[TrevorBurnham]

Description

This PR applies two micro-optimizations to getExternalProps:

• Replace Object.keys().filter() + reduce() with a simple for-in loop
• Replace indexOf() with startsWith()

My benchmarks show a ~2.5x performance improvement. This function is called on every component render for several components, so small optimizations here add up.

How has this been tested?

Existing tests provide extensive coverage for this functionality.

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

---

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.