Refactor featurize() to eliminate Union types and cast() calls

[Copilot]

What does this changes

Refactors Featurizer.featurize() in pythainlp/tokenize/han_solo.py to eliminate type casting and Union types, addressing PR #1235 review comments.

What was wrong

The features variable was typed as Union[dict[str, int], list[str]], requiring 6 cast() calls scattered throughout the feature extraction loop for type narrowing. This violated type safety principles and created maintenance burden—any logic change required updating two code paths.

How this fixes it

Core logic now builds features in their natural representation (list of strings), converting to dict only at method exit when needed:

# Before: Union type with casting throughout
features: Union[dict[str, int], list[str]]
if return_type == "dict":
    features = {}
else:
    features = []
# ... then 6x cast() calls in the loop

# After: single type, conversion at the end
features: list[str] = []
# ... clean append operations in the loop
# Convert at return only if dict requested
return {
    "X": [{"key": 1 for key in f} for f in all_features_list] if return_type == "dict" else all_features_list,
    "Y": all_labels_int if return_type == "dict" else [str(l) for l in all_labels_int]
}

Changes:

• Single implementation of feature extraction logic
• Removed Union and cast imports
• Zero type casts in hot loop
• 4 net lines removed

Your checklist for this pull request

• Passed code styles and structures
• Passed code linting checks and unit test

Original prompt

Refactor featurize() in pythainlp/tokenize/han_solo.py based on comments in this thread #1235 (review)

Try to separate the logic, so the features variable does not have to be the Union, so we can avoid many casting.

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[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[coveralls]

coverage: 53.45% (-0.08%) from 53.533%
when pulling 64bfc99 on copilot/refactor-featurize-function
into 03b92ab on dev.

[Copilot]

Pull request overview

This PR refactors the Featurizer.featurize() method in pythainlp/tokenize/han_solo.py to eliminate Union types and cast() calls, addressing technical debt from PR #1235. The refactoring improves type safety and code maintainability by building features in a single, consistent representation and converting to the requested format only at the method's return point.

Changes:

• Eliminated Union types and 6 cast() calls by building features as list[str] throughout the method
• Improved variable naming (all_features_list, all_labels_int) for better type clarity
• Consolidated conversion logic at the end of the method, reducing code duplication