Restore caching to spectrum_integrated

[arjunsavel]

Description

I've uncommented a line that checked whether there was a cached version of the integrated spectrum.

Motivation and Context

Solves #1194

How Has This Been Tested?

N/A yet — will wait for Azure build

Screenshots (if appropriate):

N/A

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have assigned/requested two reviewers for this pull request.

[codecov]

Codecov Report

Merging #1227 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1227   +/-   ##
=======================================
  Coverage   77.71%   77.72%           
=======================================
  Files          91       91           
  Lines        5727     5728    +1     
=======================================
+ Hits         4451     4452    +1     
  Misses       1276     1276           

Impacted Files	Coverage Δ
tardis/montecarlo/base.py	86.90% <100.00%> (+0.07%)	⬆️

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