Rollup merge of #92695 - Swatinem:cover-nested, r=wesleywiser

Rollup merge of #92695 - Swatinem:cover-nested, r=wesleywiser

Add `#[no_coverage]` tests for nested functions

I was playing around a bit trying to figure out how `#[no_coverage]` behaves for nested functions and thought I might as well add this as a testcase.

The "nesting covered fn inside not covered fn" case looks pretty much as expected.

The "nesting not covered fn inside a covered fn" case however seems a bit counterintuitive.
Essentially the region of the outer function "covers" its whole lexical range. And the inner function does not generate any region at all. 🤷🏻‍♂️

r? `@richkadel`