features2d: add FAST nonmax suppression

[kalwalt]

Implement optional nonmax suppression for the FAST detector as an integrated, configurable option.

• Add option to enable or disable in the FastFeatureDetector struct.
• Implement a nonmax suppression function that removes redundant keypoints with lower response.
• Reference scoring strategy and public API from OpenCV.

Test:

• Detection with/without NMS should yield different numbers of keypoints where features cluster.

Include usage doc comment for this feature.

References: https://docs.opencv.org/4.10.0/d5/d51/group__features2d__main.html#gad06fc1fdd9bb39dcbf4b8e91172c1992