fix: reduce redundant context in apply_diff error messages

[roomote]

This PR addresses issue #5795 by reducing redundant and verbose context in apply_diff error messages.

Changes Made

• Removed redundant "Search Content" section that repeats what the model just sent
• Removed verbose "Original Content" section that consumes valuable context window space
• Kept essential "Best Match Found" section for effective debugging
• Preserved similarity score, threshold, and helpful tip to use read_file

Problem Solved

When apply_diff fails to find a match, it previously returned an excessively verbose error message that included:

1. The search content that was just sent by the model (redundant)
2. A large snippet of the original file content (noisy and context-consuming)
3. The "Best Match Found" section (the key debugging information)

This created unnecessary noise in conversation history and wasted valuable context window space.

Solution

The error message now only includes the most relevant information for debugging:

• The similarity score and threshold
• The "Best Match Found" section showing what was actually found in the file
• A tip to use read_file if needed

Testing

• ✅ All existing tests pass
• ✅ Linting passes
• ✅ Type checking passes
• ✅ No breaking changes to existing functionality

The model already has the search content it just sent, so repeating it provides no value. The large original content section forced the model to re-process irrelevant code. The "Best Match" section is the key piece of information that helps the model understand exactly what diverged and correct its next attempt.

Fixes #5795

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Important

Reduces verbosity in apply_diff error messages by removing redundant sections and retaining essential debugging information in multi-file-search-replace.ts and multi-search-replace.ts.

• Error Message Changes:
  • Removed redundant "Search Content" and "Original Content" sections in multi-file-search-replace.ts and multi-search-replace.ts.
  • Retained "Best Match Found" section for debugging purposes.
  • Preserved similarity score, threshold, and a tip to use read_file.
• Files Affected:
  • multi-file-search-replace.ts: Adjusted error message construction in applyDiff().
  • multi-search-replace.ts: Adjusted error message construction in applyDiff().
• Testing:
  • All existing tests pass.
  • Linting and type checking pass.
  • No breaking changes introduced.

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