more api for objdetect

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 97.24138% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 89.66%. Comparing base (73e6ace) to head (7c4fbeb).

Files	Patch %	Lines
lib/src/objdetect/objdetect.dart	97.24%	4 Missing :warning:

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #70 +/- ## ========================================== + Coverage 89.49% 89.66% +0.17% ========================================== Files 36 36 Lines 5167 5294 +127 ========================================== + Hits 4624 4747 +123 - Misses 543 547 +4 ```

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