fix(pgvector): add chunking to prevent long list of args in queries

[kyteinsky]

The error log for the non-chunked deletion query:

{"timestamp": "2026-03-20T11:45:29.417326+00:00", "level": "ERROR", "logger": "ccb.vectordb", "message": "Error deleting chunks, rolling back documents store deletion for source ids", "filename": "pgvector.py", "function": "delete_source_ids", "line": 438, "thread_name": "AnyIO worker thread", "pid": 2148, "version": "5.3.0", "exc_info": "Traceback (most recent call last):\n  File \"/usr/local/lib/python3.11/dist-packages/sqlalchemy/engine/base.py\", line 1967, in _exec_single_context\n    self.dialect.do_execute(\n  File \"/usr/local/lib/python3.11/dist-packages/sqlalchemy/engine/default.py\", line 952, in do_execute\n    cursor.execute(statement, parameters)\n  File \"/usr/local/lib/python3.11/dist-packages/psycopg/cursor.py\", line 117, in execute\n    raise ex.with_traceback(None)\npsycopg.OperationalError: sending query and params failed: number of parameters must be between 0 and 65535\n\nThe above exception was the direct cause of the following exception:\n\nTraceback (most recent call last):\n  File \"/app/context_chat_backend/vectordb/pgvector.py\", line 435, in delete_source_ids\n    session.execute(stmt_chunks)\n  File \"/usr/local/lib/python3.11/dist-packages/sqlalchemy/orm/session.py\", line 2351, in execute\n    return self._execute_internal(\n           ^^^^^^^^^^^^^^^^^^^^^^^\n  File \"/usr/local/lib/python3.11/dist-packages/sqlalchemy/orm/session.py\", line 2249, in _execute_internal\n    result: Result[Any] = compile_state_cls.orm_execute_statement(\n                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"/usr/local/lib/python3.11/dist-packages/sqlalchemy/orm/bulk_persistence.py\", line 2033, in orm_execute_statement\n    return super().orm_execute_statement(\n           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"/usr/local/lib/python3.11/dist-packages/sqlalchemy/orm/context.py\", line 306, in orm_execute_statement\n    result = conn.execute(\n             ^^^^^^^^^^^^^\n  File \"/usr/local/lib/python3.11/dist-packages/sqlalchemy/engine/base.py\", line 1419, in execute\n    return meth(\n           ^^^^^\n  File \"/usr/local/lib/python3.11/dist-packages/sqlalchemy/sql/elements.py\", line 527, in _execute_on_connection\n    return connection._execute_clauseelement(\n           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"/usr/local/lib/python3.11/dist-packages/sqlalchemy/engine/base.py\", line 1641, in _execute_clauseelement\n    ret = self._execute_context(\n          ^^^^^^^^^^^^^^^^^^^^^^\n  File \"/usr/local/lib/python3.11/dist-packages/sqlalchemy/engine/base.py\", line 1846, in _execute_context\n    return self._exec_single_context(\n           ^^^^^^^^^^^^^^^^^^^^^^^^^^\n  File \"/usr/local/lib/python3.11/dist-packages/sqlalchemy/engine/base.py\", line 1986, in _exec_single_context\n    self._handle_dbapi_exception(\n  File \"/usr/local/lib/python3.11/dist-packages/sqlalchemy/engine/base.py\", line 2363, in _handle_dbapi_exception\n    raise sqlalchemy_exception.with_traceback(exc_info[2]) from e\n  File \"/usr/local/lib/python3.11/dist-packages/sqlalchemy/engine/base.py\", line 1967, in _exec_single_context\n    self.dialect.do_execute(\n  File \"/usr/local/lib/python3.11/dist-packages/sqlalchemy/engine/default.py\", line 952, in do_execute\n    cursor.execute(statement, parameters)\n  File \"/usr/local/lib/python3.11/dist-packages/psycopg/cursor.py\", line 117, in execute\n    raise ex.with_traceback(None)\nsqlalchemy.exc.OperationalError: (psycopg.OperationalError) sending query and params failed: number of parameters must be between 0 and 65535\n[SQL: DELETE FROM langchain_pg_embedding WHERE langchain_pg_embedding.collection_id = %(collection_id_1)s::UUID AND langchain_pg_embedding.id IN (%(id_1_1)s::VARCHAR, %(id_1_2)s::VARCHAR, %(id_1_3)s::VARCHAR, %(id_1_4)s::VARCHAR, %(id_1_5)s::VARCHAR, %(id_1_6)s::VARCHAR, %(id_1_7)s::VARCHAR, %(id_1_8)s::VARCHAR, %(id_1_9)s::VARCHAR, %(id_1_10)s::VARCHAR, %(id_1_11)s::VARCHAR, %(id_1_12)s::VARCHAR, %(id_1_13)s::VARCHAR, %(id_1_14)s::VARCHAR, ...

raise ex.with_traceback(None)\nsqlalchemy.exc.OperationalError: (psycopg.OperationalError) sending query and params failed: number of parameters must be between 0 and 65535