fix(cubesql): Split __user WHERE predicate into separate filter node

[MazterQyou]

Check List

• Tests has been run in packages where changes 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 adds an optimizer that splits meta filters (WHERE __user...) into a separate Filter node. This helps with queries where filter contains expressions that cannot be pushed down to CubeScan. In this case SQL push down is applied but meta filters should go into CubeScan anyway. Related tests are included.

[codecov]

Codecov Report

Attention: Patch coverage is 95.34884% with 12 lines in your changes missing coverage. Please review.

Project coverage is 83.69%. Comparing base (9d1c3f8) to head (6e1a008).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
.../compile/engine/df/optimizers/filter_split_meta.rs	94.82%	12 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8812      +/-   ##
==========================================
+ Coverage   83.65%   83.69%   +0.03%     
==========================================
  Files         227      228       +1     
  Lines       81773    82016     +243     
==========================================
+ Hits        68409    68640     +231     
- Misses      13364    13376      +12     

Flag	Coverage Δ
cubesql	83.69% <95.34%> (+0.03%)	⬆️

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[mcheshkov]

Let's rebase on fresh master and land it