Update protocol to Hangzhou

[dorranh]

Once Hangzhou is released on mainnet (I think this should happen within the next week or so), we should upgrade the protocol in our project (used for sandbox, tests, etc.). This will likely involve:

• [x] Updating the version of flextesa we are building in our Earthfile (+flextesa target). It looks like flextesa has simplified their build process, so we can also likely simplify our fairly manual build steps at the same time, relying on their Makefile instead.
• [x] Updating the protocol in checker_client.checker.start_local_sandbox
• [ ] Updating the default protocol in scripts/compile-ligo.rb. Alternatively, we can also remove this from the script since we are not measuring the contract size on CI anymore (instead measuring the serialized entrypoints themselves).

[dorranh]

Closed in #315 (not that I think that we might want to just remove the tezos-client calls in compile-ligo since we no longer really use that functionality.

[gkaracha]

not that I think that we might want to just remove the tezos-client calls in compile-ligo since we no longer really use that functionality.

Ah, yes, this has come up before. I'd be OK with either (a) removing the calls to tezos-client, or (b) restoring the tezos-client dependency so that we actually get to see again the size the contracts we generate.