fix: address NaN output in weight interpolation

[michaelawyu]

Description of your changes

This PR fixes an issue where weight interpolation will yield a NaN value when a property is of the same value across the fleet.

I have:

• [x] Run make reviewable to ensure this PR is ready for review.

How has this code been tested

• [x] Integration tests
• [x] E2E tests

Special notes for your reviewer

Unit tests for the file have not been checked in before; will submit a separate PR.

[michaelawyu]

Note: the fix itself has been checked in with an earlier PR; closing this one as its content has been included in #887.