Move all RPC calls to single client that chooses WS/HTTP

[peterbroadhurst]

EVMConnect has both a HTTP and a WebSocket configuration.

When a WebSocket configuration exists, the block listener connects the WebSocket and then begins to use it.

However, the rest of the listener code continues to use the HTTP connection - meaning we end up with a split where detection of blocks is pinned to a sticky connection over a WebSocket, but the remaining calls happen over HTTP relying on sticky-session HTTP load balancing for calls that require server-side context like eth_newFilter / eth_getFilterChanges.

This PR introduces a common RPC layer that all aspects of the connector use, which then perform RPC method based selection of whether to send requests down a WebSocket or HTTP connection.

A mix still has benefits:

• High volume submission can utilize concurrent HTTP connections such as eth_sendRawTransaction
• Calling read operations like eth_call can use multiple backend nodes
• Expensive calls like debug_traceTransaction can be moved off of the WebSocket

However, the mix previously used was not ideal.

So the approach here is to have a mode switch that supports:

1. ws everything is pushed down the WebSocket once estsablished
2. http everything is pushed down HTTP - only use of WebSocket is subscriptions (shoulder taps for new blocks)
3. auto a new split that is documented in detail in this PR - the new default
4. legacy as close as possible to the existing split, with two differences documented in the code