Feat/clarity cli execute json

[hstove]

Description

This PR implements some functionality that I've been using to develop a tool for running running Clarity tests in a JS environment. It's built on top of clarity-js-sdk, but it uses the raw Clarity hex result of different contract interactions. This allows for more robust handling of contracts, without having to write a parser for Clarity output.

It adds two new commands to the clarity-cli CLI:

• eval_at_chaintip_json: just like eval_at_chaintip, but it returns a JSON-serialized output to stdout, with a field for the raw Clarity hex result
• execute_json: like execute, but it returns JSON to stdout, along with the raw Clarity hex result

Type of Change

• New feature
• Bug fix
• API reference/documentation update
• Other

[jcnelson]

While I agree that clarity_cli would be improved by printing out a machine-readable result, I don't think this is best achieved by adding new commands. Instead, I think the invoke_command function should simply return the data to be displayed -- either a serde::Value or a Vec<String> -- based on the presence or absence of a --json flag. I'm already working on this.

[jcnelson]

Going to go ahead and close this -- #2597 supersedes it.