fix: table cache invalidation

[agupta-meltano]

The existing table_cache.pop clears the wrong layer: get_table_columns reads through a long-lived cached Inspector, and snowflake-sqlalchemy memoises columns per schema on it, so a table created after that schema was first reflected stays invisible and raises NoSuchTableError. Adding SnowflakeConnector.invalidate_table_cache(), which pops the table_cache entry and sets _inspector = None so reflection re-queries Snowflake, and routes SnowflakeSink.setup() two table_cache.pop calls through it fixes sqlalchemy.exc.NoSuchTableError: ().

[ReubenFrankel]

Related to MeltanoLabs#389