feat: FFF for file search

[dmtrKovalenko]

Issue for this PR

Closes #<you guys know right?>

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

This implements fff pickers for the all file search operation - file search, content search, directories & mixed search.

If you paste a large clearly AI generated description here your PR may be IGNORED or CLOSED!

How did you verify your code works?

bun test
bun dev .
bun run bench-fff.ts

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

If you do not follow this template your PR will be automatically rejected.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Potential Duplicate PRs Found

Based on the search results, there are several related PRs addressing FFF (file search) functionality:

1. feat(search): add runtime-aware search service with fff #23890 - feat(search): add runtime-aware search service with fff

   • Likely related: Implements runtime-aware FFF search service

2. feat(core): add fff-backed search service #22458 - feat(core): add fff-backed search service

   • Likely related: Adds FFF-backed search service infrastructure

3. feat: switch file search to fff #18419 - feat: switch file search to fff

   • Likely related: Earlier PR about switching file search to FFF

These PRs may already address the same feature (FFF for file search) or provide overlapping implementations. I recommend reviewing them to understand the current state of FFF file search implementation before merging PR #25160.