Allow assert with custom message to be used in const contexts

[zhassan-aws]

Description of changes:

Currently, Kani fails to compile programs that use the assert macro with a custom message in a const context, e.g.

const fn my_const_fn(x: i32, y: i32) {
    assert!(x + y == 8, "message");
}

#[cfg_attr(kani, kani::proof)]
fn main() {
    let x = 5;
    let y = 3;
    my_const_fn(x, y);
}

This is due to Kani's overridden definition of the assert macro that uses the format_args macro, which cannot yet be used in a const context.

This PR switches the assert macro definition to use the panic macro instead, which achieves the same effect (parsing of the format argument and emitting any associate warnings/errors).

Resolved issues:

Resolves #1586

Related RFC:

Optional #ISSUE-NUMBER.

Call-outs:

Testing:

• How is this change tested? Added a new test

• Is this a refactor change? No

Checklist

• Each commit message has a non-empty body, explaining why the change was made
• Methods or procedures are documented
• Regression or unit tests are included, or existing tests cover the modified code
• My PR is restricted to a single feature or bugfix

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.