Configure codecov to only check src/ files for patch coverage

The codecov/patch check was failing at 96.42% because it was checking
coverage of test files in addition to source files. Test files with
conditional imports (like pytest.importorskip("xdist")) would be
skipped in some CI configurations, causing those test lines to appear
as "not covered".

This change configures codecov to only require 100% coverage for
source files (src/), which is the standard practice. Test file
coverage should not be required.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: treyshaffer

codecov.yml

@@ -9,5 +9,7 @@ coverage:
     patch:
       default:
         target: 100%  # require patches to be 100%
+        paths:
+          - "src/"  # only check source files, not test files
     project: false
 comment: false