fix: Prevent calling contract functions from outside the contract

[jfecher]

Related issue(s)

Resolves #955

Description

Summary of changes

Prevents referencing items defined within a contract's scope from outside of a contract. Note that this currently will still allow calling these functions within another contract in the same program.

Dependency additions / changes

Test additions / changes

Updated contracts test to no longer reference contract functions within main.

Checklist

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt with default settings.
• I have linked this PR to the issue(s) that it resolves.
• I have reviewed the changes on GitHub, line by line.
• I have ensured all changes are covered in the description.

Documentation needs

• This PR requires documentation updates when merged.

Additional context

[kevaundray]

LGTM - one small nit

[critesjosh]

@jfecher I see this required docs updates. What pages need updating and what info should I add/remove?

[jfecher]

@critesjosh I don't believe we have contracts documented at all in the book yet. Once we do, we'll need to add a note that you cannot call these contract functions from outside a contract.