feat(bigframes): Support unstable sort_values, sort_index

[TrevorBergeron]

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Fixes #<issue_number_goes_here> 🦕

[gemini-code-assist]

Code Review

This pull request implements stable sorting support by adding a kind parameter to sort_values and sort_index methods and updating the underlying core logic to handle sorting stability. The review feedback recommends centralizing the list of stable sort algorithms into a constant for better maintainability and suggests several refinements to type hints and default values in method overloads. Furthermore, the reviewer identified an opportunity to propagate the kind parameter when sorting DataFrames along the column axis to ensure consistent behavior.

[tswast]

Neat use of an existing pandas parameter! (https://pandas.pydata.org/docs/reference/api/pandas.Series.sort_values.html#pandas.Series.sort_values)

Interesting opportunity here too with regards to the default in pandas not being a stable sort.