Ensure consistent embeddings are used

[ahuang11]

Closes #1210

If stored chunks was embedded with a certain embeddings model, but re-opened with another embeddings model, on query, it'll return no results.

[codecov]

Codecov Report

Attention: Patch coverage is 77.58621% with 13 lines in your changes missing coverage. Please review.

Project coverage is 55.86%. Comparing base (47a6a47) to head (cd9b01d).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
lumen/ai/vector_store.py	72.34%	13 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1214      +/-   ##
==========================================
+ Coverage   55.80%   55.86%   +0.05%     
==========================================
  Files         113      113              
  Lines       17089    17152      +63     
==========================================
+ Hits         9537     9582      +45     
- Misses       7552     7570      +18     

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[amaloney]

small change to remove duplicated code, otherwise approved