core: Audit num module for int/uint

* count_ones/zeros, trailing_ones/zeros return u32, not usize
* rotate_left/right take u32, not usize
* RADIX, MANTISSA_DIGITS, DIGITS, BITS, BYTES are u32, not usize

Doesn't touch pow because there's another PR for it.

[breaking-change]

src/test/run-pass/vector-sort-panic-safe.rs

@@ -53,7 +53,7 @@ impl Drop for DropCounter {
 }
 
 pub fn main() {
-    assert!(MAX_LEN <= std::usize::BITS);
+    assert!(MAX_LEN <= std::usize::BITS as usize);
     // len can't go above 64.
     for len in 2..MAX_LEN {
         for _ in 0..REPEATS {