#3648 refactor: Annotate `config` as an immutable mapping in more places Pull request opened by edgarrmondragon SSIA Summary by Sourcery Annotate configuration parameters and properties as read-only mappings across SQL connectors and samples to better reflect immutability in type hints. Enhancements: • Update SQL connector and schema converter APIs to accept generic Mapping types instead of mutable dict for configuration values. • Adjust sample BigQuery and SQLite connectors to use Mapping in get_sqlalchemy_url signatures, aligning them with the core connector interface. • Return a MappingProxyType directly for plugin config to reflect an immutable configuration mapping in type annotations. meltano/sdk