Add support for WinPython environments via System Python manager

[karthiknadig]

Need Statement

PET (Python Environment Tools) can discover WinPython environments, but this extension does not currently handle the WinPython environment kind. WinPython is a portable Python distribution for Windows that should be treated as a system Python installation.

Proposed Solution

Enable the System Python manager (builtin manager) to handle WinPython environments, similar to how it handles other system Python installations like WindowsStore, WindowsRegistry, and GlobalPaths.

Acceptance Criteria

• Add winpython to the NativePythonEnvironmentKind enum in nativePythonFinder.ts
• Update the builtin manager's refreshPythons filter in utils.ts to include WinPython environments
• WinPython environments discovered by PET appear in the Python Environments view
• Users can select and use WinPython as a base Python for creating virtual environments
• WinPython environments are correctly identified with appropriate display names

Technical Notes

• PET has a pet-winpython crate that discovers WinPython installations
• WinPython should use the same code path as other system Pythons (WindowsRegistry, GlobalPaths, etc.)
• No separate manager is needed - this is a minor enhancement to the existing builtin manager