Fix text finder crash from unbounded memory use

[davidalecrim1]

• Fixes After executing the command text finder:toggle, the Zed editor will freeze. #60238.
• The text finder could spike memory into the tens of gigabytes and crash the app. The finder was copying the full matched line into every match it kept, so memory grew with the number of matches times the size of each line. Enough matches carrying enough text and the process runs out of memory.

Solution

• Stop storing line text on matches. Each match now keeps only its position and column, and the text shown in a row is built lazily for the visible rows, using a bounded slice around the match rather than the whole line. Line boundaries come from the buffer's line index instead of re-scanning the content per match.
• Cap the number of matches the finder builds while streaming results, using the same ceiling project search already applies. This keeps the finder from ever assembling an unbounded match list on the UI thread.
• Behavior is unchanged: every occurrence is still its own row, jumping to a match lands on the exact line and column, and the rendered text and highlighting look the same. The finder just no longer holds text proportional to the match count.

Testing

• Added tests covering the new behavior: the match count is capped while streaming, every occurrence below the ceiling still becomes its own match at the correct line and column, and the rendered slice around a match stays bounded on a huge line while still covering a whole short line.
• Verified by hand with the reproduction from the issue. The screenshot below shows the memory usage and the matching against the issue data:

Self-Review Checklist:

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

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Release Notes:

• Fixed a crash and high memory usage in the text finder.