feat(cubestore-driver): improve WebSocket connection error messages

[ovr]

Add ConnectionError class to wrap WebSocket errors with CubeStore context, making it easier to diagnose connection failures.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 55.16%. Comparing base (fd8a312) to head (da5112e).
⚠️ Report is 4 commits behind head on master.

❗ There is a different number of reports uploaded between BASE (fd8a312) and HEAD (da5112e). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (fd8a312)	HEAD (da5112e)
cubesql	1	0

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #10355       +/-   ##
===========================================
- Coverage   77.99%   55.16%   -22.83%     
===========================================
  Files         469      221      -248     
  Lines       91781    17295    -74486     
  Branches     3539     3539               
===========================================
- Hits        71582     9541    -62041     
+ Misses      19704     7259    -12445     
  Partials      495      495               

Flag	Coverage Δ
cube-backend	55.16% <ø> (ø)
cubesql	?

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