Release candidate for v0.6.4

This release includes a number of fixes, especially to support newer versions of Python (3.9+)

Full Changelog: v0.6.3...v0.6.4-rc.4

v0.6.4

Full Changelog: v0.6.3...v0.6.4

Patch for non-hashable but serializable functions

Add fallback to `base_encoder` when serializing functions

Things like callable Pydantic models may not be serializable with the
function serializer but still serializable with the base encoder.

v0.6.2

[pyproject.toml] Fix classifier "Typing :: Typed"