Lektorlib

Type Annotations

- Narrow the return type of `lektorlib.recordcache.get_or_create_virtual`.
- Convert `lektorlib.query.PrecomputedQuery` to a generic type.

- Added type annotations
- Use PDM instead of setuptools to build distribution
- Configured pre-commit
- Run black and reorder-python-imports on the code

Fixes for Lektor 3.4 (in pre-release).

We now test under Lektor 3.3 and Lektor 3.4 (pre-release).

Drop support for python < 3.7. Test under python 3.10.

No code changes.

Release is now classified as "production/stable".

Initial release.