fix: add type check before calling .match() on diffItem.content (#6905) (#6906)

* fix: add type check before calling .match() on diffItem.content

Fixes #6905 - Error during diff application "v.content.match is not a function"

- Added type check to ensure diffItem.content is a string before calling .match()
- Added comprehensive tests for handling non-string content values
- Prevents runtime errors when content is null, undefined, or other non-string types

* fix: validate content type earlier in diff parsing

- Move type check to where content is first extracted from XML
- Remove redundant check since content is now guaranteed to be string
- Add test for early content validation

* chore: remove comments

* fix: add TelemetryService mock to multiApplyDiffTool tests

* fix: add captureDiffApplicationError to TelemetryService mock

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Co-authored-by: Roo Code <[email protected]>
Co-authored-by: daniel-lxs <[email protected]>
Co-authored-by: Daniel <[email protected]>

Author: 3 people