Further improvement on hopli

[QYuQianchen]

Hopli improvement PR #6023 had the following TODOs:

• New feature: create a Multicall ERC777 recipient contract which accepts minted and transferred wxHOPR tokens while forwarding calldata to the Multicall and executing the data payload. This will effectively mitigate the above-mentioned security concern.
• Should not do unwrap() at all, unless a previous is_ok() check is present.
• prefix all hopli env vars with HOPLI_ to prevents mixing up environment variables with other tools.
• It'd be ideal to have docs comments start with a capital letter. You can generate the docs with cargo doc --no-deps in the workspace root and browse through the generated content in the browser.
• Make get_provider_with_signer a trait based impl signature instead

Originally posted by @QYuQianchen in #5884 (comment)