Fix Expression input_mapping query optimization bug

[jaychia]

Closes #534

[codecov]

Codecov Report

Merging #536 (920d673) into main (3c99fbb) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #536      +/-   ##
==========================================
- Coverage   72.92%   72.91%   -0.02%     
==========================================
  Files          95       95              
  Lines        7638     7638              
==========================================
- Hits         5570     5569       -1     
- Misses       2068     2069       +1     

Impacted Files	Coverage Δ
daft/expressions.py	92.74% <100.00%> (-0.59%)	⬇️
daft/logical/optimizer.py	96.86% <0.00%> (+0.89%)	⬆️