Reformat Python code with yapf. (#2589)

I've add an option to yapf to do what we want for long lines, see
https://github.com/google/yapf/pull/1177.  We can now have a real Python
formatter, yay!

To make this PR, I ran my modified yapf over the repository, then looked
over the full diff.  Where yapf was mangling the param list of long
function decls/calls (mostly kernels), I manually added `#` to put
linebreaks where we want.  I fixed up other formatting too -- mostly
adding or removing a trailing comma from lists.

Overall, trailing `#` was sufficient to get formatting similar to our
current code.  I didn't have to disable yapf anywhere.

---------

Co-authored-by: Phil Tillet <phil@openai.com>

python/examples/copy_strided.py

@@ -4,8 +4,8 @@ import triton.language as tl
 
 # triton kernel
 @triton.jit
-def kernel(X, stride_xm,
-           Z, stride_zn,
+def kernel(X, stride_xm,  #
+           Z, stride_zn,  #
            BLOCK_M: tl.constexpr, BLOCK_N: tl.constexpr):
     off_m = tl.arange(0, BLOCK_M)
     off_n = tl.arange(0, BLOCK_N)

python/examples/empty.py

@@ -10,4 +10,4 @@ def kernel(X, stride_xm, stride_xn, BLOCK: tl.constexpr):
 
 
 X = torch.randn(1, device="cuda")
-pgm = kernel[(1,)](X, 1, 1, BLOCK=1024)
+pgm = kernel[(1, )](X, 1, 1, BLOCK=1024)