Implement IssuedOrNative struct

[kevin-pease]

✨ What kind of change does this PR introduce? (Bug fix, feature, docs update...)

Fixes #108.

• Moves the IssuedOrNative struct to request models, making it available throughout the crate;
• Updates several fields in request structs in 2 endpoints, so that they use this new IssuedOrNative struct;
• Updates relevant parameter building methods;
• Adds a few tests to test new parameter buidling;
• Updates relevant documentation code examples.

Note: One commit in this PR is dedicated to a large set of formatting corrections. This is because of a pre-commit hook running cargo fmt.

🤔 Checklist before submitting

• All projects build
• Follows style guide lines
• Relevant documentation was updated
• Rebased onto current main