Allow overriding Codex package versions (#39298)

## What changed

- Add `--package-version` to set the version written to `codex-package.json`, while retaining the workspace package version as the default.
- Reject values that are not runtime-compatible semantic versions, including overflowing numeric components and numeric prerelease identifiers with leading zeroes.
- Document the new option.

## Testing

- Add unit coverage for valid release, prerelease, and build versions, plus malformed and out-of-range values.

GitOrigin-RevId: cee996a6721e3fac9bd88f0bc0302a7ec7d2b2fb

scripts/codex_package/test_cli.py

@@ -0,0 +1,48 @@
+#!/usr/bin/env python3
+
+import argparse
+from pathlib import Path
+import sys
+import unittest
+
+sys.path.insert(0, str(Path(__file__).resolve().parents[1]))
+
+from codex_package.cli import parse_package_version
+
+
+class PackageVersionTest(unittest.TestCase):
+    def test_accepts_release_prerelease_and_build_versions(self) -> None:
+        for version in (
+            "0.0.0",
+            "1.2.3",
+            "0.0.0-internal.deadbeef",
+            "1.2.3-alpha.1+build.01",
+            "18446744073709551615.0.0",
+        ):
+            with self.subTest(version=version):
+                self.assertEqual(parse_package_version(version), version)
+
+    def test_rejects_versions_the_runtime_cannot_parse(self) -> None:
+        for version in (
+            "",
+            "1",
+            "1.2",
+            "1.2.3.4",
+            "v1.2.3",
+            "01.2.3",
+            "1.02.3",
+            "1.2.03",
+            "1.2.3-",
+            "1.2.3-alpha..1",
+            "1.2.3-01",
+            "1.2.3+",
+            "1.2.3+build..1",
+            "18446744073709551616.0.0",
+        ):
+            with self.subTest(version=version):
+                with self.assertRaises(argparse.ArgumentTypeError):
+                    parse_package_version(version)
+
+
+if __name__ == "__main__":
+    unittest.main()