uint8, uint16, uint32, and uint64 in kernels (#413)

A forthcoming PR will update the RNG to use these types.

Also:
- Add tests for the `//`, `<<`, and `>>` operators.
- Change `TensorWrapper` to unwrap objects when the resulting object would be simpler.
- Clean up `throw_unreachable`, since it was triggering compiler warnings.

python/test/unit/language/test_random.py

@@ -147,6 +147,7 @@ def test_rand(size, seed, device='cuda'):
     N = x.numel()
     grid = (triton.cdiv(N, BLOCK),)
     kernel[grid](x, N, seed)
+    assert all((x >= 0) & (x <= 1))
     assert scipy.stats.kstest(x.tolist(), 'uniform', args=(0, 1)).statistic < 0.01
 
 # test normal PRNG