[red-knot] Fix gradual equivalence for callable types

[dhruvmanila]

Summary

As mentioned in #16698 (comment), part of #15382, this PR updates the is_gradual_equivalent_to implementation between callable types to be similar to is_equivalent_to and checks other attributes of parameters like name, optionality, and parameter kind.

Test Plan

Expand the existing test cases to consider other properties but not all similar to how the tests are structured for subtyping and assignability.

[github-actions]

mypy_primer results

No ecosystem changes detected ✅

[carljm]

Looks great! I really like the pattern you've established of using a common function with a callback that implements the distinction between subtyping and assignability (or in this case, equivalence and gradual equivalence.)