[red-knot] Use iterative approach to collect overloads (#17607)
## Summary
This PR updates the `to_overloaded` method to use an iterative approach
instead of a recursive one.
Refer to
https://github.com/astral-sh/ruff/pull/17585#discussion_r2056804587 for
context.
The main benefit here is that it avoids calling the `to_overloaded`
function in a recursive manner which is a salsa query. So, this is a bit
hand wavy but we should also see less memory used because the cache will
only contain a single entry which should be the entire overload chain.
Previously, the recursive approach would mean that each of the function
involved in an overload chain would have a cache entry. This reduce in
memory shouldn't be too much and I haven't looked at the actual data for
it.
## Test Plan
Existing test cases should pass.
