Add FastCV Allocator and DSP Initialization Functions

[quic-apreetam]

This PR introduces the FastCV allocator and DSP initialization functions to optimize memory allocation and DSP operations in OpenCV.

Changes:

• Added getDefaultFastCVAllocator() function to retrieve the default FastCV allocator optimized for DSP.

• Added fastcvq6init() and fastcvq6deinit() functions to initialize and deinitialize the FastCV DSP environment.

• Implemented sumOfAbsoluteDiffs() function to calculate the sum of absolute differences using FastCV.
  Additional APIs will be added after the first review from this implementation.

Note: This PR is not ready for merging unless the changes look good. It is intended for review and feedback

Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
• The PR is proposed to the proper branch
• There is a reference to the original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
• The feature is well documented and sample code can be built with the project CMake

[quic-apreetam]

In modules/fastcv/test/test_sad_dsp.cpp, we are explicitly releasing memory to be able to call cv::fastcv::dsp::fastcvq6deinit();