Avoid conditional compilation and move old version to legacy_vonmises
Small clean up
Additional comments

Apply vonmises fix only to Generator
Add tests for correctness

closes #17378
closes #17275

Cast to avoid warnings
Correct function

Most compilers should optimize it, but it doesn't hurt to inline and has a better name
now.

Assert that an invalid value (2**n-1 for n = 8, 16, 32, 64) has not
been passed to the Lemire function.

When the input to Generator.integers was 2**32, the value 2**32-1
was being passed as the `rng` argument to the 32-bit Lemire method,
but that method requires `rng` be strictly less then 2**32-1.

The fix was to handle 2**32-1 by calling next_uint32 directly.
This also works for the legacy code without changing the stream
of random integers from `randint`.

Closes gh-16066.