Run llvm-cov in release so coverage finishes under 6h

Debug+instrumented `-m test -u all` spent 5.5h on 41 tests. Use
--release, a 120s per-test timeout, and -j0. Bound the suite step
at 180 minutes so a hang still leaves time to report.

Assisted-by: Grok:4.6

.github/workflows/cron-ci.yaml

@@ -22,6 +22,7 @@ jobs:
   codecov:
     name: Collect code coverage data
     runs-on: ubuntu-latest
+    timeout-minutes: 350
     # Disable this scheduled job when running on a fork.
     if: ${{ github.repository == 'RustPython/RustPython' || github.event_name != 'schedule' }}
     env:
@@ -41,15 +42,18 @@ jobs:
 
       - run: sudo apt-get update && sudo apt-get -y install lcov
 
+      # llvm-cov of a debug binary makes `-m test -u all` take many hours per
+      # dozen tests. Release + per-test timeout keeps the job under 6h.
       - name: Run cargo-llvm-cov with Rust tests.
-        run: cargo llvm-cov --no-report --workspace --exclude rustpython_wasm --exclude rustpython-venvlauncher --exclude rustpython-capi --verbose --no-default-features --features stdlib,importlib,stdio,encodings,ssl-rustls-aws-lc,jit,host_env
+        run: cargo llvm-cov --no-report --release --workspace --exclude rustpython_wasm --exclude rustpython-venvlauncher --exclude rustpython-capi --verbose --no-default-features --features stdlib,importlib,stdio,encodings,ssl-rustls-aws-lc,jit,host_env
 
       - name: Run cargo-llvm-cov with Python snippets.
         run: python scripts/cargo-llvm-cov.py
         continue-on-error: true
 
       - name: Run cargo-llvm-cov with Python test suite.
-        run: cargo llvm-cov --no-report run -- -m test -u all --slowest --fail-env-changed
+        timeout-minutes: 180
+        run: cargo llvm-cov --no-report --release run -- -m test -u all --timeout 120 --slowest --fail-env-changed -j0
         continue-on-error: true
 
       - name: Prepare code coverage data

scripts/cargo-llvm-cov.py

@@ -7,7 +7,15 @@ TARGET = "extra_tests/snippets"
 def run_llvm_cov(file_path: str):
     """Run cargo llvm-cov on a file."""
     if file_path.endswith(".py"):
-        command = ["cargo", "llvm-cov", "--no-report", "run", "--", file_path]
+        command = [
+            "cargo",
+            "llvm-cov",
+            "--no-report",
+            "--release",
+            "run",
+            "--",
+            file_path,
+        ]
         subprocess.call(command)