replace uses of np.ndarray with npt.NDArray (#681)

Summary:
Pull Request resolved: #681

X-link: pytorch/captum#1389

X-link: pytorch/botorch#2586

X-link: pytorch/audio#3846

This replaces uses of `numpy.ndarray` in type annotations with `numpy.typing.NDArray`. In Numpy-1.24.0+ `numpy.ndarray` is annotated as generic type. Without template parameters it triggers static analysis errors:
```counterexample
Generic type `ndarray` expects 2 type parameters.
```
`numpy.typing.NDArray` is an alias that provides default template parameters.

Reviewed By: ryanthomasjohnson

Differential Revision: D64619891

fbshipit-source-id: dffc096b1ce90d11e73d475f0bbcb8867ed9ef01

Author: igorsugak

opacus/accountants/analysis/prv/prvs.py

@@ -16,6 +16,7 @@
 from typing import Tuple
 
 import numpy as np
+import numpy.typing as npt
 from scipy import integrate
 from scipy.special import erfc
 
@@ -133,7 +134,7 @@ def mean(self) -> float:
 
 @dataclass
 class DiscretePRV:
-    pmf: np.ndarray
+    pmf: npt.NDArray
     domain: Domain
 
     def __len__(self) -> int: