This should make it easier to add new entries as well as clarifying
the intent of this filter.

In Python 3.13 the `locals` function now returns a fresh mapping
each time it's called (when called in a function). We thus need
to store a reference to the mapping being used, rather than
re-fetching it each time.

Since we don't actually need to modify the locals within the scope
of the test function itself, it suffices to use our own mapping
here rather than the result of calling `locals`, which fully
isolates this test from the nature of that function.

Fixes davidhalter#2002

This moves to using the 3.13 grammar as well as testing 3.13 in CI.

Jedi passes pickles to subprocesses which are running the target
version of Python and thus may not be the same as the version
under which Jedi itself is running. In Python 3.13, pathlib is
being refactored to allow for easier extension and has thus moved
most of its internal implementation to a submodule. Unfortunately
this changes the paths of the symbols, causing pickles of those
types to fail to load in earlier versions of Python.

This commit introduces a custom unpickler which accounts for this
move, allowing bi-directional passing of pickles to work.

See davidhalter#2012 for details.