Performance of --fork could be improved with memoization

[area]

Expected Behavior

When forking a provider, ganache-core should only have to query the provider once for the code/nonce/balance that exists at a particular address at the safeBlockNumber. As the response will not change, any repeated lookups should be cached.

Current Behavior

Even if ganache has queried the code/nonce/balance at a particular address and block number before, it will query the provider again despite the fact this will not have changed

Possible Solution

Memoize the calls to the fallback provider, as I have done here, for example.

Context

While testing upgrades for our dapp, we wish to fork mainnet to test against the current state, but we see a large number of repeated calls to infura when we open our dapp and browse around against our forked ganache-cli - not good for them, or our API limits!

[davidmurdoch]

Ah, nice. This looks great! I'm assuming this works because forking always passes a blockNumber and never a tag like "latest"?

If you want to write some tests for these memoized methods I'd love to pull this in!

[area]

I think this has effectively been done in #581 and can be closed.