Avoid xarray to cast ints to float64 just to add a NaN

[spiani]

No description provided.

[Copilot]

Pull request overview

This PR aims to prevent xarray from decoding integer river maps into float64 (to represent missing values as NaN) when generating OB indices, reducing unnecessary dtype changes and associated overhead.

Changes:

• Adjust xarray.open_dataset usage for reading the rivers variable to disable masking/scaling.
• Update a debug log message in OB indices generation.
• Reduce logging noise by raising the numba logger level.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/mitgcm_inputs/ob_indices/ob_indices.py	Tweaks a debug log message emitted during boundary strip extraction.
src/mitgcm_inputs/ob_indices/__init__.py	Changes how the rivers dataset is opened to avoid xarray masking/scaling behavior.
src/mitgcm_inputs/__main__.py	Adds numba to the list of loggers whose verbosity is reduced.

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