add Topk to tensor (#9343)

* terrible but somewhat working impl

* linux behaves differently than macos?

* slightly better impl

* small clean up; haven't figured this out yet

* better

* torch has different behavior on linux and macos for duplicated values

* add sum docs

* fix test

* add torch return_type test

* add an exception test

* wrap_fxn instead, and move op lower in order

* better repeated values test

* rerun ci

docs/tensor/ops.md

@@ -34,6 +34,7 @@
 ::: tinygrad.Tensor.interpolate
 ::: tinygrad.Tensor.scatter
 ::: tinygrad.Tensor.scatter_reduce
+::: tinygrad.Tensor.topk
 
 ## Neural Network (functional)