Fix PyEnv section endlessly spinning when pyenv is not installed

[Copilot]

Issue

When pyenv is not installed on a user's machine, the PyEnv section in the Python Environments view shows an infinite loading spinner when expanded:

Root Cause

In the refreshPyenv function, when pyenv is not found initially, the code tries to get it from the NativePythonFinder data. However, it doesn't check if any pyenv managers were found before trying to access managers[0].executable:

if (pyenv === undefined) {
    const managers = data
        .filter((e) => !isNativeEnvInfo(e))
        .map((e) => e as NativeEnvManagerInfo)
        .filter((e) => e.tool.toLowerCase() === 'pyenv');
    pyenv = managers[0].executable; // Error when managers is empty
    await setPyenv(pyenv);
}

This causes an error when pyenv is not installed, leaving the UI in an infinite loading state.

Fix

Added a check to ensure the managers array has elements before trying to access the first one:

if (pyenv === undefined) {
    const managers = data
        .filter((e) => !isNativeEnvInfo(e))
        .map((e) => e as NativeEnvManagerInfo)
        .filter((e) => e.tool.toLowerCase() === 'pyenv');
    
    if (managers.length > 0) {
        pyenv = managers[0].executable;
        await setPyenv(pyenv);
    }
}

This ensures the UI doesn't get stuck in a loading state when pyenv is not installed on the system.

Fixes #437.

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[karthiknadig]

registerEnvironmentManager should not be called if pyenv is not found on the machine.

[Copilot]

registerEnvironmentManager should not be called if pyenv is not found on the machine.

I've updated the code to ensure registerEnvironmentManager is only called when pyenv is found on the machine. Previously, we were only checking for exceptions but not validating the return value of getPyenv(). The fix (fc8f621) ensures we only register the PyEnv manager when a valid pyenv executable is found.

comments addressed.