Clean up remnants of #110395

[fee1-dead]

#110395 left us with many test cases that have been disabled because the standard library traits that used to be const are not anymore.

For these cases we should:

• Find out if they can be written without depending on the traits or impls being const. If they can, rewrite them and re-enable them.
• If they can't be written without depending on impl const or const traits, constify the relevant traits and impls where possible. Re-enable them