Strip and safer conversion of values to float to avoid error see HEA-615

[girum-air]

No description provided.

[girum-air]

There was a “ “ a space instead of ““ in cell BN218 of CD16_14Nov24 file and that trips up the float conversion code for that row for max value.

[rhunwicks]

@girum-air I realised that there were some other inconsistencies in this code, in that we were only converting the value to a percentage when the wealth characteristic is percentage_of_households, but we were converting min/max for any numbers less than 1. Therefore I pushed another commit because it seems easier than explaining. I also raised a better error message if the conversion fails.

Please can you review.

[girum-air]

@rhunwicks I approved! Can't do it in the UI cause it was my PR originally