Fix auto-detection by not setting PYTHON_VERSIONS when not specified

The auto-detection wasn't working because the
CLI was always setting PYTHON_VERSIONS environment variable to all supported
versions when --python-versions was not provided.

Changes:
- click_helpers.py: Return None instead of all versions when option not provided
- helpers.py: Only set PYTHON_VERSIONS env var when explicitly specified
- main.py: Update type hints to allow None for python_versions parameter

Now the flow works correctly:
1. No --python-versions CLI option -> python_versions = None
2. None passed to Docker -> no PYTHON_VERSIONS env var set
3. Container auto-detects installed versions using pyenv
4. Tests run only on detected versions

python/docker/test_wheels/scripts/src/opm_wheels/click_helpers.py

@@ -6,9 +6,10 @@ from opm_wheels import helpers
 
 def validate_python_versions(
     ctx: click.Context, param: Union[click.Option, click.Parameter], value: str
-) -> list[PythonVersion]:
+) -> list[PythonVersion] | None:
     if value is None:
-        value = ",".join(PythonVersion.valid_versions())
+        # Return None to allow runtime auto-detection of installed versions
+        return None
     versions = value.split(",")
     versions = [PythonVersion.from_str(str(v)) for v in versions]
     valid_versions = [PythonVersion.from_str(v) for v in PythonVersion.values()]

python/docker/test_wheels/scripts/src/opm_wheels/helpers.py

@@ -129,7 +129,7 @@ def run_docker_build(
 def run_docker_run(
     docker_tag: str,
     wheel_dir: Path,
-    python_versions: list[PythonVersion],
+    python_versions: list[PythonVersion] | None,
     host_tests_dir: Path = None,
     test_cases_common: str = None,
     test_cases_simulators: str = None,
@@ -140,9 +140,16 @@ def run_docker_run(
         "docker", "run",
         "--rm",
         "-v", str(wheel_dir) + ":/test/wheels/",
-        "-e", "PYTHON_VERSIONS=" + ",".join([str(v) for v in python_versions])
     ]
 
+    # Only set PYTHON_VERSIONS environment variable if explicitly specified
+    # If not specified (None), let the container auto-detect installed versions
+    if python_versions is not None:
+        docker_cmd.extend(["-e", "PYTHON_VERSIONS=" + ",".join([str(v) for v in python_versions])])
+        logging.info(f"Using specified Python versions: {','.join([str(v) for v in python_versions])}")
+    else:
+        logging.info("Using auto-detected Python versions from container")
+
     # Add host test directory mounts if specified
     if host_tests_dir:
         # Validate that the expected directories exist

python/docker/test_wheels/scripts/src/opm_wheels/main.py

@@ -170,7 +170,7 @@ def build_docker_image(
 def run_docker_image(
     docker_os: str,
     wheel_dir: str,
-    python_versions: list[PythonVersion],
+    python_versions: list[PythonVersion] | None,
     host_tests_dir: Path = None,
     test_cases_common: str = None,
     test_cases_simulators: str = None,