Make environmentPath consistently reference the Python executable

[Copilot]

PythonEnvironmentInfo.environmentPath could reference either an environment directory or its Python executable, forcing consumers to handle manager-specific semantics. This change defines and returns the executable URI consistently.

Changes

• Environment discovery

  • Use discovered executable paths for Conda, Pipenv, Poetry, pyenv, and venv environments.
  • Ignore malformed Conda records without a prefix.
  • Preserve legacy Pipenv selections stored as environment prefixes.

• Prefix-dependent operations

  • Use sysPrefix for Conda package management, deletion, .gitignore creation, and CONDA_PREFIX comparisons.
  • Use sysPrefix when removing virtual environments.

• Public API

  • Clarify that environmentPath identifies the Python executable.
  • Update API package version and changelog.

environmentPath: Uri.file(info.executable),
sysPrefix: info.prefix,

• Fixes environmentPath should always return the path to the executable #1804