fix: Raise on duplicated aliases

[gab23r]

Raises an ImplementationError when a schema contains columns with duplicate aliases.

Motivation

I was using LLM to generate dataframely schemas, it gives me duplicated alias like in:

class MySchema(dy.Schema):
    a = dy.Int64(alias="a")
    b = dy.Int64(alias="a")

It could be nice from dataframely it icould raise in this case.

Changes

• Detect duplicate aliases within a single schema
• Detect duplicate aliases when inheriting from a parent schema
• Add tests for both cases

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (b3edd6a) to head (08efe2b).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #291   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
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  Files           54        54           
  Lines         3121      3127    +6     
=========================================
+ Hits          3121      3127    +6     

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[Copilot]

Pull request overview

This PR adds early validation to schema definition to prevent ambiguous schemas where multiple Columns resolve to the same effective column name (via alias), raising ImplementationError during class creation and adding regression tests.

Changes:

• Raise ImplementationError when two columns in the same schema resolve to the same name (alias or attribute name).
• Raise ImplementationError when a child schema introduces a column whose resolved name clashes with an inherited one.
• Add tests covering both same-schema and inherited duplicate-alias scenarios.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
dataframely/_base_schema.py	Adds duplicate-name checks during metadata collection/merging to raise ImplementationError early.
tests/columns/test_alias.py	Adds tests asserting duplicate aliases are rejected for same-schema and inherited definitions.

[AndreasAlbertQC]

Thanks @gab23r !