Support loading artifact from hardhat deployments directory

[taminomara]

Part of #563.

Allow loading artifacts from hardhat deployments directory by scanning its contents and parsing all allowed contracts.

[bh2smith]

So far only reviewed hardhat dot rs. This is very long. Will have to come back later for more.

[taminomara]

I can move example into a separate PR, it that will help with review.

[nlordell]

The artifact loading code (load_from_directory) was very linear and easy to review.

One meta-PR comment, I think that the example could have been done in a separate PR, so this one could focus on the relevant ethcontract-common/src/artifact/hardhat.rs changes. I see that the unit test does depend on the new example output making it hard to split the two, but maybe its worth having manually created test hardhat deployment directory somewhere (kind of like an assertion of "this is the expected format and layout for a deployment directory").

[nlordell]

I can move example into a separate PR, it that will help with review.

TBH that would be kind of nice (if it isn't too much effort), I admittedly did not review the example carefully at all. If its too much work, don't worry about it.

[taminomara]

Yeah this is difficult to review, I'll split the PR. I wish github allowed tree view the same way Intellij github plugin does.

[taminomara]

I've moved example into a separate PR which I'll publish after this one. Filtering contracts by name and unrelated changes to documentation are moved to a separate PR as well.

[taminomara]

From +13,914 −10,346 to +221 −99, way better!