chore: Split Kokoro presubmit into lint and coverage jobs.

PiperOrigin-RevId: 915500963

Author: speedstorm1

.kokoro/presubmit/coverage.cfg

@@ -0,0 +1,13 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+# Run unit tests to generate coverage data, then run the coverage aggregation and threshold check
+env_vars: {
+    key: "NOX_SESSION"
+    value: "unit-3.13 cover"
+}
+
+# Run unit tests in parallel, splitting up by file, and track coverage metrics
+env_vars: {
+    key: "PYTEST_ADDOPTS"
+    value: "-n=auto --dist=loadscope --cov=google --cov-append --cov-config=.coveragerc --cov-report= --cov-fail-under=0 --tb=no"
+}