Fix iotools tests for pandas 3

[kandersolar]

• Closes iotools test failures with pandas 3 #2728
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• Tests added
• Updates entries in docs/sphinx/source/reference for API changes.
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Pretty straightforward. The only complexity is bridging the gap between pandas 2 strings (dtype('O')) and pandas 3 strings (<StringDtype(storage='python', na_value=nan)>). We could explicitly check the installed pandas version and select the appropriate dtype, but I opted to just let pandas infer the right one from the test values.

[kandersolar]

Ready for review. The only iotools failure was a rate limiting issue.

I disagree with the linter flag and am ignoring it.