fix(nominal): support non-zero-based category labels in functional metrics (#3460)

[Sayyam-Akram]

What does this PR do?

Fixes #3460

• Remaps unique categorical labels in functional nominal metrics (cramers_v, pearsons_contingency_coefficient, theils_u, tschuprows_t, and their _matrix versions) to contiguous 0-based indices before updating the confusion matrix.
• Casts confmat to float in _compute_chi_squared before applying Yates' continuity correction to prevent Long-to-Float in-place addition RuntimeError.
• Adds unit tests verifying behavior on non-zero-based category labels across all nominal metrics.

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• Was this discussed/agreed via a Github issue?
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• Did you write any new necessary tests?