Wwestgarth/add contracts endpoint

[wwestgarth-enclave]

Description

Problem:
We have the endpoint v1/perps/contracts that contain useful market data for each perpetual-futures markets. The end-point also contains an isClosed field which can be used to determine whether the underlying market for RWA's are closed.

Given we want to roll out more RWA alpha-strats etc. etc. it would make sense for this field to be available to any strat-managers that are using the python client.

Solution:
Add methods on the enclave-python client to call into the contracts endpoint. I have also added the equivalent endpoint for spot markets.

Testing/Examples:
Locally ran the following:

def main():

    # create a client
    enclave_client = Client(API_KEY, API_SECRET, enclave.models.SANDBOX)
    if not enclave_client.wait_until_ready():
        raise RuntimeError("Enclave not connecting.")
    
    print(enclave_client.perps.get_contracts().json())
    print(enclave_client.spot.get_ticker().json())