chore: explicitly import CurveTrait for sub trait method and remove some default implementations

[asterite]

Description

Problem

Noir will soon require trait methods to be in scope to be used.

In this test this line:

    let result = point.dbl().dbl().sub(point);

uses the sub method for the CurveTrait. Because there's also sub from std::ops::Sub, Noir now doesn't know which one to use. This PR will fix it for the upcoming release.

Summary

In addition to using that import, I removed the default implementations of add and others because those are defined separately, and those default implementations will error once noir-lang/noir#6645 is merged.

Additional Context

For now this will produce a warning, but I guess it's fine (it will be gone when this feature is released)

PR Checklist

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.