[NNC] Change fuseLoops API to return bool flag and not throw any exceptions (#56353)
Summary:
Partial fix for https://github.com/pytorch/pytorch/issues/56357
Changes the `fuseLoops` API to the following form:
```
static bool fuseLoops(const std::vector<For*>& loops, For** fused);
```
Also, adds a new API to check for loop-carried dependences:
```
static bool hasLoopCarriedDependence(For* loop);
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/56353
Reviewed By: bertmaher
Differential Revision: D27856214
Pulled By: navahgar
fbshipit-source-id: 443557088692585657faee296602c547a00117dd
