Metal Unary: Add benchmarks and process kernels in a tile based fashion (#2056)

* add basic unary bench for sqrt

* process unary commands in tiles of 4

* re-enable all benchmarks

* rename helper to unary

* modify approach to split up tiled and non-tiled operations

* undo bench ignore for other tests

* update tile size to 2

* only perform the optimization on the contiguous even numbered element case

candle-core/benches/benchmarks/mod.rs

@@ -3,6 +3,7 @@ pub(crate) mod conv_transpose2d;
 pub(crate) mod matmul;
 pub(crate) mod qmatmul;
 pub(crate) mod random;
+pub(crate) mod unary;
 pub(crate) mod where_cond;
 
 use candle_core::{Device, Result};