This change adds full return-type and parameter-type annotations to all ~625 functions and methods across the entire virtualenv source tree. It brings the codebase from ~26% type coverage to near-complete coverage, matching the standard already established in the sibling tox project.

Key changes include:

• PEP 561 marker: Added py.typed so downstream consumers get inline type information.
• Ruff ANN rules enabled: Replaced the blanket "ANN" ignore in pyproject.toml with only the two specific exceptions (ANN003, ANN401), and added FBT001 to the global ignore since the existing boolean-positional-argument function signatures are public API.
• ty type checker hardened: Added --error-on-warning to both type and type-3.8 tox environments in tox.toml.
• All modules annotated: config, run, create (including CPython/PyPy/GraalPy/RustPython builders), activation (all 7 shells), seed (pip install, wheels, periodic update), app_data, util (lock, path, subprocess, zipapp), and discovery — every function now has explicit parameter types and return types.
• Both linters pass clean: ruff check and ty check --python-version 3.14 --error-on-warning report zero errors. All pre-existing tests continue to pass.

Fixes: #3075

Thanks for contributing, make sure you address all the checklists (for details on how see development documentation)

• ran the linter to address style issues (tox -e fix)
• wrote descriptive pull request text
• ensured there are test(s) validating the fix
• added news fragment in docs/changelog folder
• updated/extended the documentation