reimplement sqrt and isqrt in pure vyper and remove them from builtins

[cyberthirst]

Simple Summary

Move sqrt and isqrt builtins to pure Vyper so that they're implementation is easier to verify and remove complexity from the compiler codebase.

Motivation

Builtins are a major source of complexity in the compiler codebase and have caused many codegen bugs in the past (for example, see: GHSA-5jrj-52x8-m64h). Pure Vyper is more accessible for general audience and thus has higher chance of being further audited.

Additionally, sqrt is implemented via a special inlining mechanism which imposes the need to often handle it via special edge-cases (for example, see: #4219 (comment)).

Specification

We suggest making sqrt and isqrt pure library functions.

Backwards Compatibility

This is a breaking change, the builtins would have to be explicitly imported from the standard library.

[charles-cooper]

in terms of scoping, i would say we should start with sqrt() because of the inlining mechanism

[cyberthirst]

one thing we might have to deal with is selective imports. that would enable importing sqrt as a function(eg from stdlib.math import sqrt)
edit: updated example