Add support for conv_transpose2d on Metal backend (#1903)

* add support for conv transpose 2d and add bench mark for float types

* update bench calculation

* enable testing all conv operations on metal

candle-core/benches/benchmarks/mod.rs

@@ -1,4 +1,5 @@
 pub(crate) mod affine;
+pub(crate) mod conv_transpose2d;
 pub(crate) mod matmul;
 pub(crate) mod random;
 pub(crate) mod where_cond;