Implement Send + Sync for GraphImpl/Operation.
Implement Send + Sync for GraphImpl/Operation.

According to the Tensorflow C API documentation:

  Graphs may be shared between sessions. Graphs are thread-safe when
  used as directed below.

Which presumably means when you use the C API as intended --- the C
API uses a mutex to control graph access/modification.

tensorflow/rust,tensorflow/rust,tensorflow/rust,adamcrume/tensorflow-rust,adamcrume/tensorflow-rust,adamcrume/tensorflow-rust,adamcrume/tensorflow-rust,tensorflow/rust