`read_gdal`: switch back to gdal kwargs to leverage its subsetting capability

[scottstanie]

Description of proposed changes

general quality-of-life fixes that came up while adding more GPS comparisons for UTM products (these are before those additions, it just because a big enough PR to submit)

• Typos/unused import fixes that were highlighted by my spellchecker
• Starting the use again of the subsetting capability of ReadAsArray instead of reading everything (https://github.com/insarlab/MintPy/pull/661), since the errors in the comment were from this: https://github.com/OSGeo/gdal/issues/8026 (but can be avoided by casting to a python numeric type)
• simplify logic in update_attribute_or_not to exit early
• backwards compatible changes to readfile functions to allow more functions to accept pathlib.Paths

Reminders

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