creates TorClient class and _RequestManager base class

[0xfMissingNo]

was going to make TorClient for myself; noticed some TODOs that'd look like would helpful to knock out. lmk and I'll remove the TorClient

In [1]: from dydx3.constants import API_HOST_MAINNET

In [2]: from dydx3 import TorClient as Client

In [3]: public_client = Client(
   ...:     host=API_HOST_MAINNET,
   ...: )

In [4]: public_client.public.get_markets()
Out[4]: 
{'markets': {'FIL-USD': {'market': 'FIL-USD',
   'status': 'ONLINE',
   'baseAsset': 'FIL',
   'quoteAsset': 'USD',
   'stepSize': '0.1',