chore(cubesql): Improve error handling

[MazterQyou]

Check List

• Tests have been run in packages where changes have been made if available
• Linter has been run for changed code
• Tests for the changes have been added if not covered yet
• Docs have been added / updated if required

Description of Changes Made

This PR improves error handling, unwrapping an onion of nested DataFusion and Arrow errors, and adding information regarding whether the error happened in the database execution or post-processing steps.

[codecov]

Codecov Report

❌ Patch coverage is 22.07792% with 60 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.06%. Comparing base (77bbe2e) to head (5c9d92d).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
rust/cubesql/cubesql/src/sql/postgres/shim.rs	20.40%	39 Missing ⚠️
rust/cubesql/cubesql/src/compile/engine/df/scan.rs	25.00%	21 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #10118       +/-   ##
===========================================
+ Coverage   55.17%   78.06%   +22.89%     
===========================================
  Files         213      457      +244     
  Lines       16904    91078    +74174     
  Branches     3335     3335               
===========================================
+ Hits         9326    71101    +61775     
- Misses       7100    19499    +12399     
  Partials      478      478               

Flag	Coverage Δ
cube-backend	55.17% <ø> (ø)
cubesql	83.28% <22.07%> (?)

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[ovr]

Probably, we need to box DataFusionError, ArrowError. I assume it's a large enum. Can we add 1-liner tests with assert_eq for mem::size_of<ConnectionError>. Thanks

[MazterQyou]

I have tested this and CubeError is the variant of biggest size. DataFusionError and ArrowError actually happen to be the smallest, so I avoided boxing them in the end. I added the mem::size_of test to verify this.

[ovr]

LGTM, minor nit, related to Boxing + check sizeof