Refactor: Extract type parsing and typed conversion into parser.py

Move TypeNode, TypeSignatureParser, and TypedValueConverter into a new
pyathena/parser.py module. TypedValueConverter receives converter
dependencies via constructor injection to avoid circular imports.
Also moves _split_array_items to parser.py as a shared parsing utility.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: laughingman7743