V7 support for request batching

[fselmo]

What was wrong?

Closes #832

How was it fixed?

Add batch request support to the RequestManager via a context manager. Expose this as a high-level API on the Web3 / AsyncWeb3 class itself (w3.batch_requests()).

Todo:

• [x] Handle / skip EthereumTesterProvider test case
• [x] Handle IPC & WS provider batch request cases
• [x] Handle persistent connection provider cases
• [x] Clean up commit history
• [x] Add entry to the release notes
• [ ] Add or update documentation related to these changes -- separate PR ?

Cute Animal Picture

[fselmo]

This is good for an initial review. It's still missing documentation but that may be best in a separate PR? Thoughts there? Usage examples can be seen in the tests for now.