fix: DH-21843: Fix unexpected code studio unmount

[dgodinez-dh]

• added unit test that mimics the race condition of the bug
• added unit test for expected behavior when a layout should change
• change DashboardLayout lastConfig to a ref

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 49.77%. Comparing base (53e35dd) to head (2098a8c).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2672      +/-   ##
==========================================
- Coverage   49.78%   49.77%   -0.02%     
==========================================
  Files         774      774              
  Lines       43917    43946      +29     
  Branches    11129    11330     +201     
==========================================
+ Hits        21866    21873       +7     
- Misses      22033    22054      +21     
- Partials       18       19       +1     

Flag	Coverage Δ
unit	49.77% <100.00%> (-0.02%)	⬇️

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[mofojed]

Looks good, thanks.