ci: revert to goveralls for coverage reporting

Reverted coverage reporting to use goveralls tool (like the original
implementation) instead of the GitHub Action. This approach provides
better control over which packages are included in coverage metrics.

Changes:
- Install goveralls tool before coverage generation
- Filter packages to exclude: gotests/gotests, testdata, templates
- Use -coverpkg flag to specify which packages to measure
- Upload to Coveralls using goveralls command
- Changed coverage file back to coverage.out
- Keep Codecov upload for dual reporting

This matches the original coverage approach from commit 3dcf5ef but
updated for modern Go versions (1.22-1.25).

The filtered coverage focuses on library packages:
- github.com/cweill/gotests (main library)
- internal/goparser
- internal/input
- internal/models
- internal/output
- internal/render

Excludes CLI and test data packages from coverage metrics.

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

Co-Authored-By: Claude <noreply@anthropic.com>

Author: cweill

.github/workflows/go.yml

@@ -30,23 +30,27 @@ jobs:
     - name: Test
       run: go test -v ./...
 
-    - name: Coverage
+    - name: Coverage Dependencies
+      if: matrix.go == '1.25.x'
+      run: go install github.com/mattn/goveralls@latest
+
+    - name: Coverage Reporting Generation
       if: matrix.go == '1.25.x'
       run: |
-        go test -v -covermode=count -coverprofile=coverage.txt -coverpkg=./... ./...
+        export PKGS=$(go list ./... | grep -vE "(gotests/gotests|.*data|templates)" | tr -s '\n' ',' | sed 's/.\{1\}$//')
+        go test -v -covermode=count -coverpkg=$PKGS -coverprofile=coverage.out ./...
 
     - name: Upload coverage to Coveralls
       if: matrix.go == '1.25.x'
-      uses: coverallsapp/github-action@v2
-      with:
-        github-token: ${{ secrets.GITHUB_TOKEN }}
-        path-to-lcov: coverage.txt
+      run: goveralls -coverprofile=coverage.out -service=github
+      env:
+        COVERALLS_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
     - name: Upload coverage to Codecov
       if: matrix.go == '1.25.x'
       uses: codecov/codecov-action@v5
       with:
         token: ${{ secrets.CODECOV_TOKEN }}
-        files: ./coverage.txt
+        files: ./coverage.out
         fail_ci_if_error: false
         verbose: true