fix: memoization issue in SplitPane component

[Omriruvio]

This commit fixes an issue with the useMemo hook in the SplitPane component, which was causing a warning about the size of the memoized array changing between renders. The issue was caused by variables that were not memoized and were changing on each render.

To fix the issue, we memoized the variables that were causing the issue using the useMemo hook, including children, propSizes, and wrapSize. This ensures that these variables are not recreated on each render, preventing the warning about the size of the memoized array changing.

Additional minor type corrections were made.