fix: Handle ambiguous column names in chart queries

[sentry]

This PR addresses the InvalidRequestError: Ambiguous column name 'SUM(program_sequence_number)' in result set column descriptions that occurred when generating chart data.

Problem:
The error arose because the chart query builder could generate SQL queries with duplicate column aliases (e.g., two SUM(program_sequence_number) columns). This happened when multiple metrics with identical aggregation and column names (and no explicit unique aliases) were included in a chart request. SQLAlchemy's dict(row) conversion then failed to process the result set due to these ambiguous column names.

Solution:
An internal helper function, _ensure_unique_alias, has been introduced in ddpui/core/charts/charts_service.py. This function takes an alias and a set of already seen aliases, returning a unique version of the alias by appending numeric suffixes (e.g., _2, _3) if a collision is detected.

This helper is now applied at all points where metric aliases are determined and used for both SQL query generation (in build_multi_metric_query) and for constructing the column_mapping (in execute_chart_query and execute_saved_chart_query). This ensures that all generated SQL column aliases are unique, preventing the InvalidRequestError during result set processing.

Fixes DALGO-BACKEND-2FX

[sentry]

Codecov Report

❌ Patch coverage is 50.00000% with 8 lines in your changes missing coverage. Please review.
✅ Project coverage is 58.65%. Comparing base (75cb6fd) to head (b81eea6).

Files with missing lines	Patch %	Lines
ddpui/core/charts/charts_service.py	50.00%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1384      +/-   ##
==========================================
- Coverage   58.66%   58.65%   -0.01%     
==========================================
  Files         132      132              
  Lines       15690    15706      +16     
==========================================
+ Hits         9205     9213       +8     
- Misses       6485     6493       +8     

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