Ensure prediction explanations are json-serializable

[eccabay]

Closes #2366

Since the writing of this issue, a couple other data types also caused issues, so I added those as well.

[codecov]

Codecov Report

Merging #3262 (33e4bd4) into main (992b877) will increase coverage by 0.1%.
The diff coverage is 100.0%.

@@           Coverage Diff           @@
##            main   #3262     +/-   ##
=======================================
+ Coverage   99.8%   99.8%   +0.1%     
=======================================
  Files        326     326             
  Lines      31477   31496     +19     
=======================================
+ Hits       31386   31405     +19     
  Misses        91      91             

Impacted Files	Coverage Δ
...tanding/prediction_explanations/_user_interface.py	100.0% <100.0%> (ø)
...s/prediction_explanations_tests/test_explainers.py	100.0% <100.0%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 992b877...33e4bd4. Read the comment docs.

[jeremyliweishih]

Might need some changes to the test but should be good after pending discussion!

[freddyaboulton]

Thank you for the fix @eccabay !!