Refactors GenerateHeatmap transforms for clarity

Streamlines the GenerateHeatmap and GenerateHeatmapd transforms for better usability and code clarity.

Specifically:
- Improves the input landmark array validation to provide a more descriptive error message.
- Removes example notebooks.

DCO Remediation Commit for sewon.jeon <[email protected]>

I, sewon.jeon <[email protected]>, hereby add my Signed-off-by to this commit: 8ef905b
I, sewon.jeon <[email protected]>, hereby add my Signed-off-by to this commit: 226bf90
I, sewon.jeon <[email protected]>, hereby add my Signed-off-by to this commit: 3097baf
I, sewon.jeon <[email protected]>, hereby add my Signed-off-by to this commit: 0072cb0

Signed-off-by: sewon.jeon <[email protected]>

Author: eclipse0922