Define behavior of nested pymongo.timeout call. Options:

1. nested timeout() call acts independently:

   with pymongo.timeout(1):
       client.test.test.insert_one({})
       with pymongo.timeout(5):
           client.test.test.insert_one({}) # Will timeout using the 5 second deadline
   

2. nested timeout() call can only shorten the deadline, not extend it.

   with pymongo.timeout(1):
       client.test.test.insert_one({})
       with pymongo.timeout(5):
           client.test.test.insert_one({}) # Will timeout using the original 1 second deadline
   

Option 1) violates the contract of timeout() in the sense that the block of code will not raise a timeout when the original timeout has expired so option 2) makes more sense in my opinion.

We can always add support for option 1) at a later date via a new parameter, for example:

with pymongo.timeout(1):
    client.test.test.insert_one({})
    # Shield from outer timeouts/deadlines and use 5 sec deadline:
    with pymongo.timeout(5, shield=True):
        client.test.test.insert_one({})