fix(metastore-cache): prune before add

[villebro]

SUMMARY

Currently the Metastore cache deletes expired entries after trying to add a new entry. If an expired entry exists with the same key, this will cause the operation to fail. This PR fixes the issue, and adds a new test that would previously have failed.

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.72%. Comparing base (76d897e) to head (94ba822).
Report is 1094 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #29301       +/-   ##
===========================================
+ Coverage   60.48%   83.72%   +23.23%     
===========================================
  Files        1931      518     -1413     
  Lines       76236    37548    -38688     
  Branches     8568        0     -8568     
===========================================
- Hits        46114    31438    -14676     
+ Misses      28017     6110    -21907     
+ Partials     2105        0     -2105     

Flag	Coverage Δ
hive	48.94% <0.00%> (-0.23%)	⬇️
javascript	?
mysql	77.22% <100.00%> (?)
postgres	77.33% <100.00%> (?)
presto	53.55% <0.00%> (-0.25%)	⬇️
python	83.72% <100.00%> (+20.23%)	⬆️
sqlite	76.79% <100.00%> (?)
unit	59.24% <0.00%> (+1.61%)	⬆️

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