Add edge case tests for text handling

[cardmagic]

Summary

Add comprehensive edge case tests across all components to improve test coverage and document expected behavior.

Tests Added

Bayes (10 tests)

• Empty string training/classification
• Unicode text handling
• Emoji in text
• Special characters only
• Very long text (10k repetitions)
• Single word classification
• Whitespace-only input
• Mixed case handling
• Numbers in text

LSI (8 tests)

• Empty/single item index behavior
• remove_item functionality
• remove_item on nonexistent item
• items method
• find_related excludes self
• Unicode mixed with ASCII
• needs_rebuild? with auto_rebuild
• categories_for nonexistent item

Extensions (18 tests)

• without_punctuation method (5 tests)
• sum_with_identity with block and custom identity
• Vector magnitude (basic, zero vector, single element, negative values)
• Vector normalize (basic, unit vector, preserves direction)
• Matrix diag, trans alias, element assignment

Coverage

Metric	Before	After
Line	91.39%	92.78%
Branch	72.64%	76.42%

Fixes #52

[Copilot]

Pull request overview

This PR adds comprehensive edge case tests to improve test coverage for the Bayes, LSI, and Extensions components. The additions focus on boundary conditions, Unicode handling, and error cases to document expected behavior and increase overall test coverage from 91.39% to 92.78% for line coverage and from 72.64% to 76.42% for branch coverage.

Key Changes:

• Added 10 edge case tests for Bayesian classifier covering empty strings, Unicode, emojis, special characters, and very long text
• Added 8 edge case tests for LSI covering index operations, item management, and category lookups
• Added 18 tests for Extensions covering string punctuation handling, vector operations, and matrix utilities

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
test/bayes/bayesian_test.rb	Added 10 edge case tests for empty strings, Unicode text, emojis, special characters, very long text, single words, whitespace-only input, mixed case, and numbers in text
test/lsi/lsi_test.rb	Added 8 edge case tests for empty/single item indexes, item removal, related item finding, Unicode handling, auto-rebuild behavior, and category lookups
test/extensions/word_hash_test.rb	Added 18 tests covering array sum methods with blocks and custom identities, string punctuation removal, vector magnitude and normalization, and matrix operations

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