[typespec-python] Add support for uv package manager alongside pip

[Copilot]

This PR adds support for the uv package manager alongside pip in the typespec-python scripts, resolving issues where the emitter would fail when working in uv-created virtual environments that don't have pip installed as a dependency.

Problem

Users working with tsp inside uv-created virtual environments encountered failures because the emitter hardcoded pip usage, even though uv could handle the package management more efficiently.

Solution

Implemented automatic package manager detection that:

• Prefers uv when available (faster, more modern)
• Falls back to pip when uv is not available
• Maintains full backward compatibility with existing pip-only environments
• Provides clear error messaging when no package manager is found

Changes Made

New Package Manager Abstraction (package_manager.py)

# Auto-detects best available package manager
package_manager = detect_package_manager()  # Returns 'uv', 'pip', or 'python -m pip'

# Provides unified installation interface
install_packages(['black'], package_manager)

Updated Installation Scripts

• install.py: Now detects and uses either uv or pip for package installations
• prepare.py: Uses package manager abstraction for dev requirements installation
• venvtools.py: Simplified by removing redundant functions while maintaining compatibility
• run_tsp.py: Made error message package manager agnostic

Usage Examples

With uv available:

# Automatically uses uv commands (faster)
uv pip install -U black

With only pip available:

# Falls back to pip (unchanged behavior)
pip install -U black

Benefits

• ✅ uv environments work out of the box - no need to install pip as dependency
• ✅ Performance improvement - uv installations are significantly faster
• ✅ Zero breaking changes - existing pip workflows unchanged
• ✅ Better error messages - clearer guidance when package managers unavailable

Testing

Comprehensive testing validates:

• Package manager detection across different environments
• Command generation for both uv and pip
• Integration with all modified scripts
• Backward compatibility with pip-only setups
• End-to-end workflow functionality

Fixes #3115.

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[msyyc]

fix microsoft/typespec#7502

[Copilot]

fix microsoft/typespec#7502

Fixed TypeSpec issue #7502 by completing the uv package manager support. Updated run_tsp.py to use the package manager abstraction instead of hardcoded pip dependency, ensuring the emitter works seamlessly in uv-created virtual environments. (58bfc70)