fix: Allow overriding column definitions in schema inheritance

[Andreas Albert (AndreasAlbertQC)]

Motivation

PR #291 introduced duplicate alias detection, but it also broke overriding column definitions in subclasses. For example, this valid pattern started raising an error:

class FirstSchema(dy.Schema):
    x = dy.Int64()

class SecondSchema(FirstSchema):
    x = dy.Int64(nullable=True)  # Override — should be allowed

Changes

Before merging the child namespace into the inherited metadata, walk the parent MRO to identify columns that share the same attribute name as a child-defined column. Remove those parent columns so the child's definition takes precedence, while still detecting genuine alias conflicts (e.g., a new column b with an alias that clashes with an inherited column a).

Validation

• test_override — new test that verifies subclass column overrides work
• test_duplicate_alias_same_schema and test_duplicate_alias_inherited_schema — existing tests still pass, confirming alias conflict detection is preserved

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (72fb1a6) to head (13f7403).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #302   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           56        56           
  Lines         3218      3230   +12     
=========================================
+ Hits          3218      3230   +12     

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[Copilot]

Pull request overview

Fixes a regression from PR #291 where duplicate-alias detection prevented legitimate subclass overrides of inherited schema columns, by adjusting schema metadata merging so child column definitions take precedence.

Changes:

• Remove inherited column entries when a subclass defines a Column with the same attribute name (override semantics).
• Add a regression test ensuring schema subclass overrides don’t raise during class creation.

Reviewed changes

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

File	Description
dataframely/_base_schema.py	Updates SchemaMeta.__new__ to drop overridden inherited columns before merging child metadata, preserving duplicate-alias conflict detection.
tests/schema/test_base.py	Adds a regression test for overriding a column definition in a schema subclass.