feat(graphql): add linesCount to ImpactedFile type

[sentry]

This PR addresses the GraphQLError: Cannot query field 'linesCount' on type 'ImpactedFile'. Did you mean 'missesCount'? by adding the linesCount field to the ImpactedFile GraphQL type.

Previously, clients attempting to query linesCount on ImpactedFile would encounter an error because this field was not defined in the schema. The total line count can be derived from the headCoverage totals (hits + misses + partials).

Changes include:

• Added linesCount: Int! to the ImpactedFile type definition in apps/codecov-api/graphql_api/types/impacted_file/impacted_file.graphql.
• Implemented a @cached_property lines_count on the ImpactedFile dataclass in apps/codecov-api/services/comparison.py. This property calculates the total lines by summing head_coverage.hits, head_coverage.misses, and head_coverage.partials. It returns 0 if head_coverage is None (e.g., for deleted files).
• Created a resolver resolve_lines_count in apps/codecov-api/graphql_api/types/impacted_file/impacted_file.py to expose this new property via the GraphQL API.

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Fixes API-EWF

_{This PR was automatically generated by Sentry. You can adjust this setting at any time.}

[thomasrockhu-codecov]

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Codecov Report

❌ Patch coverage is 50.00000% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.63%. Comparing base (a8ec2db) to head (597958d).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
apps/codecov-api/services/comparison.py	40.00%	3 Missing ⚠️
...i/graphql_api/types/impacted_file/impacted_file.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2028      +/-   ##
==========================================
- Coverage   91.63%   91.63%   -0.01%     
==========================================
  Files        1336     1336              
  Lines       53230    53238       +8     
  Branches     1647     1647              
==========================================
+ Hits        48778    48782       +4     
- Misses       4131     4135       +4     
  Partials      321      321              

Flag	Coverage Δ
apiunit	93.97% <50.00%> (-0.02%)	⬇️

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Codecov Report

❌ Patch coverage is 50.00000% with 4 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
apps/codecov-api/services/comparison.py	40.00%	3 Missing ⚠️
...i/graphql_api/types/impacted_file/impacted_file.py	66.66%	1 Missing ⚠️

❌ Your patch check has failed because the patch coverage (50.00%) is below the target coverage (90.00%). You can increase the patch coverage or adjust the target coverage.

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