Fix splitLineCount and unifiedLineCount on hunks

[amadeus]

A classic case of -- we didn't really depend on this so never totally realized it was wrong. Anyways, these values were wrong and it started showing up in my virtualization work because I depended on them.

Also added tests to make sure I don't fuck these up again

[Copilot]

Pull request overview

This PR fixes incorrect calculations for splitLineCount and unifiedLineCount on diff hunks. The previous implementation incorrectly calculated these values as simple max/count of additions and deletions without accounting for context lines. The fix properly computes these counts by iterating through hunk content and summing context lines with the appropriate calculation for change blocks.

• Updated the calculation logic to properly account for context lines in both split and unified modes
• Added comprehensive tests that verify the calculated counts match actual rendered output
• Updated all affected snapshots to reflect the corrected values

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

File	Description
packages/diffs/src/utils/parsePatchFiles.ts	Replaced simple max/count calculations with proper reduce logic that accounts for context lines in both splitLineCount and unifiedLineCount
packages/diffs/test/testUtils.ts	Updated verification logic to match new calculation method and added helper functions to count rendered lines and split rows
packages/diffs/test/parsePatchFiles.test.ts	Added two new tests that verify calculated counts match actual rendered output in both split and unified modes
packages/diffs/test/snapshots/*.snap	Updated snapshot values to reflect corrected splitLineCount and unifiedLineCount calculations across all test files

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