[#127] Use `--mode mockup` instead of remote node

Description

Problem: Currently typecheck-tezos-client.sh uses our carthagenet node. However, now it's not necessary to have node for contract typechecking.

Solution: Use --mode mockup option for tezos-client typecheck script

Related issue(s)

Resolves #127 (closed)

Resolves #126 (closed) (at least for now, this stage now again takes ~1 min)

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