add more methods to Mat, more test, add cv.sqrt, cv.sum

[rainyl]

• add: cv.sum, cv.sqrt
• Mat.iterPixel -> Mat.forEachPixel, Mat.iterRow -> Mat.forEachRow
• add: Mat.row() Mat.col() Mat.t() Mat.isSubmatrix Mat.adjustROI Mat.locateROI

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 86.36364% with 6 lines in your changes missing coverage. Please review.

Project coverage is 91.20%. Comparing base (9280b20) to head (a4f3887).

Files	Patch %	Lines
lib/src/core/mat.dart	91.42%	3 Missing :warning:
lib/src/core/size.dart	0.00%	2 Missing :warning:
lib/src/core/core.dart	85.71%	1 Missing :warning:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #185 +/- ## ========================================== + Coverage 91.12% 91.20% +0.08% ========================================== Files 56 56 Lines 8345 8372 +27 ========================================== + Hits 7604 7636 +32 + Misses 741 736 -5 ```

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