add shortcircuit in isclose for zero tolerances (#61529)
Summary:
Fixes https://github.com/pytorch/pytorch/issues/61412.
Large integers gave false positives, because the comparison always takes place in floating point dtypes. This happens, because their integer precision is lower than the range of an integer dtype with the same number of bits.
For non-extremal values, `isclose` is defined by [this equation]:
```python
abs(a - b) <= atol + rtol * abs(b)
```
For `rtol == 0 and atol==0`, this is equivalent to `a == b`. This PR goes for the low hanging fruit and adds a shortcut for this case that falls back to an actual equality check.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/61529
Reviewed By: gchanan
Differential Revision: D29707534
Pulled By: mruberry
fbshipit-source-id: 71b8c4901e9cd4f366442437e52032b0d3002b4a
