Add assert_hierarchy lint

Detect build-time assertions that can use a stronger form and suggest
the strongest applicable one.

The new lint classifies assertion conditions as `build_assert!`,
`const_assert!`, or `static_assert!` depending on whether they depend
on runtime values, generic compile-time context, or only closed
compile-time context.

Using that classification, it warns for:

- `build_assert!` -> `const_assert!`
- `build_assert!` -> `static_assert!`
- `const_assert!` -> `static_assert!`

This keeps diagnostics aligned with the documented assertion hierarchy
by preferring the earliest and most robust assertion form available.

Add `#![allow(klint::assert_hierarchy)]` in `tests/ui/build_error.rs`
and re-bless the test so that test remains focused.

Signed-off-by: Mohamad Alsadhan <mo@sdhn.cc>

Author: mqqz