ci: add functional tests to coverage + fix lcov errors

1. Add 'make check-functional-parallel' to coverage job
   - Unit tests alone cover ~27% (mostly utilities)
   - Functional tests exercise UI, XMPP, and full application flow
   - Should significantly increase coverage

2. Fix lcov errors:
   - Remove /usr/lib/* pattern (unused, causes error)
   - Add 'unused' to --ignore-errors

.github/workflows/ci-code.yml

@@ -112,11 +112,12 @@ jobs:
             ./configure --enable-coverage --enable-otr --enable-pgp --enable-omemo --enable-plugins
             make -j$(nproc)
             make check || true
+            make check-functional-parallel || true
             lcov --capture --directory . --output-file /coverage/coverage.info --ignore-errors inconsistent
             lcov --remove /coverage/coverage.info \
-              "/usr/include/*" "/usr/lib/*" "*/tests/*" \
+              "/usr/include/*" "*/tests/*" \
               --output-file /coverage/coverage.info \
-              --ignore-errors inconsistent,empty
+              --ignore-errors inconsistent,empty,unused
           '
       - name: Upload coverage to Codecov
         uses: codecov/codecov-action@v4