feat: add Pixi extension recommendation and support for Pixi environments

[eleanorjboyd]

No description provided.

[eleanorjboyd]

confirming @karthiknadig you are good with this as the notif

[Copilot]

Pull request overview

This PR adds support for detecting Pixi Python environments and recommending the Pixi extension to users. Pixi is a cross-platform package manager that provides Python environments, and this change integrates it into the Python environment discovery and prioritization system.

Changes:

• Added Pixi as a new environment kind in the native Python finder
• Implemented extension recommendation logic that prompts users to install the Pixi extension when Pixi environments are detected
• Updated manager priority sorting to include Pixi (second highest priority after pyenv)
• Added localized strings for the Pixi extension recommendation prompt

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
src/managers/common/nativePythonFinder.ts	Added pixi enum value to NativePythonEnvironmentKind
src/managers/builtin/utils.ts	Implemented recommendPixiExtension() function with session tracking and persistent state; filters out Pixi envs from builtin manager
src/common/utils/pythonPath.ts	Added Pixi to manager priority order (2nd highest); improved sorting logic for unknown managers to place them after known managers but before system
src/common/localize.ts	Added PixiStrings namespace with localized messages for extension recommendation