feat: add support for GDAL 3.9 and Python 3.12 and 3.13

[edparris]

This change adds support for GDAL 3.9 and verifying compatibility with Python versions 3.12 and 3.13. GDAL 3.9 was previously unsupported because it contained an undocumented breaking change to the structure of the xml:DES metadata that broke how our toolkit was accessing SICD/SIDD metadata. The only functional update in this commit is code that will let us work with either xml:DES structure and therefore retain compatibility with GDAL versions 3.7 through 3.9. See: OSGeo/gdal#8953 for more information.

The default tox environments have been expanded to verify these changes and maintain future compatibility. Instead of a single environment that will always pull the latest versions within an approved range, multiple environments with pinned GDAL and Proj versions have been setup and associated with the Python versions under test. This table shows the combinations currently checked with a full build:

Test Environment	GDAL	Proj
py39	3.7.0	9.2.1
py310	3.8.3	9.3.1
py311	3.8.3	9.3.1
py312	3.8.5	9.4.1
py313	3.9.2	9.5.0

The intent is to ensure this library can be deployed by customers to a variety of environments and verify compatibility with multiple GDAL versions in wide use today. We will drop support for older python versions once they reach end-of-life status. See: Status of Python Versions

Checklist

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• Code changes are compact and well-structured to facilitate easy review
• Changes are documented in the README.md and other relevant documentation pages
• PR title and description accurately reflect the changes and are detailed enough for historical tracking
• PR contains tests that cover all new code and the code has been manual tested
• All new dependencies are declared (if any), and no unnecessary libraries are added
• Performance impacts (if any) of the changes are evaluated and documented
• Security implications of the changes (if any) are reviewed and addressed
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[drduhe]

LGTM