feat: add watershed filter

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.01% :tada:

Comparison is base (f7b46a3) 98.64% compared to head (8251bb9) 98.65%.

:exclamation: Current head 8251bb9 differs from pull request most recent head 42315d6. Consider uploading reports for the commit 42315d6 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #379 +/- ## ========================================== + Coverage 98.64% 98.65% +0.01% ========================================== Files 223 224 +1 Lines 5763 5814 +51 Branches 1217 1226 +9 ========================================== + Hits 5685 5736 +51 Misses 75 75 Partials 3 3 ``` | [Files Changed](https://app.codecov.io/gh/image-js/image-js-typescript/pull/379?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=image-js) | Coverage Δ | | |---|---|---| | [src/roi/RoiMapManager.ts](https://app.codecov.io/gh/image-js/image-js-typescript/pull/379?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=image-js#diff-c3JjL3JvaS9Sb2lNYXBNYW5hZ2VyLnRz) | `100.00% <100.00%> (ø)` | | | [src/roi/computeRois.ts](https://app.codecov.io/gh/image-js/image-js-typescript/pull/379?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=image-js#diff-c3JjL3JvaS9jb21wdXRlUm9pcy50cw==) | `100.00% <100.00%> (ø)` | | | [src/roi/waterShed.ts](https://app.codecov.io/gh/image-js/image-js-typescript/pull/379?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=image-js#diff-c3JjL3JvaS93YXRlclNoZWQudHM=) | `100.00% <100.00%> (ø)` | | | [test/testUtils.ts](https://app.codecov.io/gh/image-js/image-js-typescript/pull/379?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=image-js#diff-dGVzdC90ZXN0VXRpbHMudHM=) | `100.00% <100.00%> (ø)` | |

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