[ruff_linter] - Use LibCST in adjust_indentation for mixed whitespace

[diceroll123]

Summary

The dedent_to function has a difficult time with mixed whitespace.

The code now conditionally uses the LibCST method if there is mixed whitespace.

Fixes #12707

Test Plan

cargo test

[codspeed-hq]

CodSpeed Performance Report

Merging #12740 will not alter performance

_{Comparing diceroll123:fix-RET505-indent-errors (d922997) with main (df7345e)}

Summary

✅ 32 untouched benchmarks

[github-actions]

ruff-ecosystem results

Linter (stable)

✅ ecosystem check detected no linter changes.

Linter (preview)

✅ ecosystem check detected no linter changes.

[MichaReiser]

This seems like a pretty big regression. I think I would prefer just to disable the fix in case there's mixed-indentation than regressing performance by that much.

[diceroll123]

Yeah, that is not ideal as is.

I'd like to try one more alternative approach, which does already include detecting mixed indentation.

[MichaReiser]

Nice!