Fix LSI dimension mismatch with native Ruby SVD

[cardmagic]

Summary

• Fix ExceptionForMatrix::ErrDimensionMismatch when classifying with 10+ similar documents using native Ruby SVD
• Transpose reduced matrix when native SVD returns swapped dimensions
• Iterate over columns (documents) instead of rows (terms) in build_index

Root Cause

Native Ruby SVD returns transposed dimensions when row_size < column_size (common case: few unique terms, many documents). This caused query vectors (5 elements) to be compared against document vectors (20 elements).

Test Plan

• Reproduction case from LSI dimension mismatch with large similar document sets #72 now works
• All 85 tests pass with NATIVE_VECTOR=true
• All 85 tests pass with GSL

Fixes #72

[Copilot]

Pull request overview

Fixes a dimension mismatch error (ExceptionForMatrix::ErrDimensionMismatch) that occurs when classifying documents using native Ruby SVD with 10+ similar documents. The root cause is that Ruby's native SVD implementation returns transposed dimensions when there are fewer unique terms than documents, causing query vectors to have incompatible dimensions with document vectors during comparison.

Key Changes:

• Fixed iteration to use column_size instead of row_size when building the document index
• Added dimension validation and transposition logic to handle native Ruby SVD's behavior
• Ensured consistent matrix dimensions between GSL and native Ruby implementations

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