docs(changelog): add the #1722 fragment

Co-Authored-By: Claude Fable 5.2 <[email protected]>

changelog.d/1722-cables-batched-primitives.md

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+- Submarine cables draw from a few batched primitives instead of thousands of
+  entities. Switching the layer off and back on, and zooming with it on, no
+  longer stall the page, and it holds about 900 MB less memory. Double-click
+  no longer starts Cesium's entity tracking on a cable (mazy1998, #1722).