Enhance query handling for nested columns and date filters

[gutzbenj]

• Improve nested/dotted column handling: alias nested columns with underscores for consistent querying when data is loaded via database accessors.
• Consolidate date-type filters to be ORed together when fetching data into memory, allowing multiple date conditions to apply correctly.
• Add validation to ensure filters with values specify corresponding columns.

[codecov]

Codecov Report

❌ Patch coverage is 77.77778% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.68%. Comparing base (d383522) to head (4038846).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/koality/executor.py	36.36%	7 Missing ⚠️
src/koality/models.py	72.72%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #66      +/-   ##
==========================================
+ Coverage   79.47%   84.68%   +5.21%     
==========================================
  Files           7        7              
  Lines        1179     1208      +29     
==========================================
+ Hits          937     1023      +86     
+ Misses        242      185      -57     

Flag	Coverage Δ
unittests	84.68% <77.77%> (+5.21%)	⬆️

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