Merge pull request #7275 from kpayson64/python_min_memory_cleanup

src/python/grpcio/grpc/_channel.py

src/python/grpcio/grpc/_cython/_cygrpc/call.pyx.pxi

src/python/grpcio/grpc/_cython/_cygrpc/records.pxd.pxi

src/python/grpcio/grpc/_server.py

...rpcio_tests/tests/unit/_cython/_cancel_many_calls_test.py

...sts/unit/_cython/_read_some_but_not_all_responses_test.py

src/python/grpcio_tests/tests/unit/_cython/cygrpc_test.py