Re-export names from psycopg3.types

[dlax]

This is useful to silent mypy errors when implicit reexport is disabled
(e.g. in strict mode) like:

error: Module 'psycopg3.types' does not explicitly export attribute
'Jsonb'; implicit reexport disabled  [attr-defined]

https://mypy.readthedocs.io/en/stable/command_line.html#cmdoption-mypy-no-implicit-reexport

Accordingly, we import Int4 from psycopg3.types directly in
test_copy.py.

[dvarrazzo]

Aww, that's so cumbersome to maintain... But I don't see other options here, right?

[dlax]

Another option is to write each import as: from .module import Symbol as Symbol

[dvarrazzo]

I was thinking about that. It' still quite the duplication but at least it's local and there is not a long unstructured list at the bottom of the file.

[dlax]

Ok; changed to import X as X.

Also, there's an open question at python/mypy#10198 for that "issue".

[dvarrazzo]

Yes, redundant but I feel better about the more localised duplication. Thank you: will merge!