Bug: fix an issue with string keys in left and semi joins in Dask, add Dask to tpch benchmarks

[raisadz]

What type of PR is this? (check all applicable)

• 💾 Refactor
• ✨ Feature
• 🐛 Bug Fix
• 🔧 Optimization
• 📝 Documentation
• ✅ Test
• 🐳 Other

Related issues

• Related issue #
• Closes #

Checklist

• Code follows style guide (ruff)
• Tests added
• Documented the changes

If you have comments or can explain your changes, please do so below.

• Fix an issue with string keys in left and semi joins in Dask;
• Added an error message of Expr.unique is not supported for the Dask backend as it modifies the index;
• Added Dask to tpch benchmarks;

[FBruzzesi]

Thanks for the PR, and adjusting the tpch queries to handle the dask unique case.

I left a major comment that will need to be addressed though 😇

[FBruzzesi]

Thanks @raisadz 🙌🏼

[MarcoGorelli]

awesome work here, thanks both! 🙌