feat: add DataFrame|LazyFrame.cast method

[FBruzzesi]

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

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

Checklist

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

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

Additionally extends Expr|Series.cast with strict argument

[FBruzzesi]

Unrelated CI failure

[MarcoGorelli]

thanks @FBruzzesi !

are we sure we need this? I think this can currently be accomplished with with_columns and Expr.cast, no? e.g.

df.with_columns(nw.all().cast(nw.String))

or

df.with_columns(nw.col(col).cast(dtype) for col, dtype in dtypes.items())

?

i'm just a little unsure about expanding the DataFrame / LazyFrame API when there's a simple Expr solution

[FBruzzesi]

i'm just a little unsure about expanding the DataFrame / LazyFrame API when there's a simple Expr solution

Fair enough!

Polars exposed it, it is a nice ergonomic shortcut I am reaching out for, but definitly there is an Expr workaround

[FBruzzesi]

Closing as not planned for now

[MarcoGorelli]

sure, thanks - we can always reconsider later

[FBruzzesi]

Yep, agree! This PR has so many conflicts that even if we want to consider adding it, it would be just easier to write it from scratch.

I am trying to do some cleanup, especially before sprints 😁