project: Add CRLF regex search integration test

[Copilot]

The .crlf(true) RegexBuilder option (added alongside the fancy-regex 0.18.0 bump) makes ^/$ anchors in multiline mode match before \r\n pairs, not just bare \n. Without it, patterns using $ anchors silently fail to match in CRLF files.

Important nuance uncovered during testing: .crlf(true) in fancy-regex only affects ^/$ anchors and . — it does not make \n in a pattern match \r\n. Cross-line patterns targeting CRLF files should use \r?\n to handle both endings.

Changes

• Adds test_multiline_regex_crlf to crates/project/tests/integration/search.rs, covering the pattern ^hello$\r?\n against CRLF text. The $ + .crlf(true) anchors correctly before \r\n; without CRLF mode the \r prevents $ from firing and the pattern never matches.
• Moves the use language::Buffer import from inside each test function to file-level.

Self-Review Checklist:

• I've reviewed my own diff for quality, security, and reliability
• Unsafe blocks (if any) have justifying comments
• The content is consistent with the UI/UX checklist
• Tests cover the new/changed behavior
• Performance impact has been considered and is acceptable

Release Notes:

• N/A