[#281] [#53] Add `getStorage` to morley-client and `checkStorage` to cleveland

Description

This MR adds the ability to check a contract's storage to the nettest eDSL.

Note: Storages with big_map cannot be retrieved, due to a limitation in the RPC's /storage endpoint, which returns the big_map's ID instead of its contents. To prevent misuse, we use the UnpackedValScope t constraint, which implies HasNoBigMap t.

Related issue(s)

Resolves #281 (closed)

Resolves part of #53 (closed)

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