Add Python Appender for scalar create, append, flush and close

[daviddallakyan2005]

Python still has no Appender. This adds conn.appender(table, schema=None, catalog=None) with append, flush, close, a context manager, and column_count, for scalar types.

Follows #369

This is the first of three stacked PRs. Chunks: #586. Query appender: #587.

append() converts each cell to a Value and uses the C++ row Append API. Use append_chunk for bulk inserts, which writes into vectors in place. append_chunk is #586.

This does not change conn.append(table, df).

How to test

OVERRIDE_GIT_DESCRIBE=v1.5.5
.venv/bin/pytest tests/fast/test_appender.py tests/fast/test_insert.py tests/fast/test_context_manager.py tests/fast/test_module.py -q

After this commit: 9 new tests in tests/fast/test_appender.py passed. Insert, context manager, and module tests also passed.

On the full stack I also ran tests/fast excluding spark: 1655 passed. Two failures (missing reraise fixture, missing typing_extensions for experimental spark) fail the same way on current main.