Fix Session bulk mappings typing for mapped classes

Fix Session bulk mappings typing for mapped classes

Fixes #9256.

This updates the annotations for Session.bulk_insert_mappings() and Session.bulk_update_mappings().

The docstrings and runtime behavior already allow either a mapped class or a Mapper object, but the previous annotations only accepted Mapper[Any].

This patch switches those arguments to the existing _EntityBindKey alias, which matches the inputs accepted by _class_to_mapper(): mapped classes and Mapper objects, but not AliasedClass or AliasedInsp.

I also updated the internal _bulk_save_mappings() annotation so the public methods and the private helper stay consistent. The scoped_session proxy output has been kept in sync with tools/generate_proxy_methods.py, and the generator check passes.

I added a typing regression test covering both mapped classes and Mapper objects for the two bulk mapping methods. I confirmed that the mapped-class cases fail with the old annotation and pass with this change.

Checked locally:

python -m pytest -m mypy test/typing/test_mypy.py -k "session.py" -q
python -m mypy ./lib/sqlalchemy
python tools/generate_proxy_methods.py --check
python -m pytest test/orm/dml/test_bulk.py -q
python -m pytest -m mypy test/typing/test_mypy.py -k "not typed_queries.py" -q

I could not run the full typing suite locally because my local Python 3.12 environment does not include string.templatelib. I only skipped typed_queries.py; that file is expected to be covered by SQLAlchemy's Python 3.14 mypy CI job.

Closes: #13322
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/13322
Pull-request-sha: bb730f34275a7c40c94e668ecda1131804ba3084

Change-Id: I4c5d516b3933b4e7fae9c844881a61f557a8bb5e