Add arrow_try_cast UDF

[adriangb]

Which issue does this PR close?

N/A - new feature

Rationale for this change

arrow_cast(expr, 'DataType') casts to Arrow data types specified as strings but errors on failure. try_cast(expr AS type) returns NULL on failure but only works with SQL types. There's currently no way to attempt a cast to a specific Arrow type and get NULL on failure instead of an error.

What changes are included in this PR?

Adds a new arrow_try_cast(expression, datatype) scalar function that combines the behavior of arrow_cast and try_cast:

• Accepts Arrow data type strings (like arrow_cast)
• Returns NULL on cast failure instead of erroring (like try_cast)

Implementation details:

• Reuses arrow_cast's data_type_from_args helper (made pub(crate))
• Simplifies to Expr::TryCast during optimization (vs Expr::Cast for arrow_cast)
• Registered alongside existing core functions

Are these changes tested?

Yes — new sqllogictest file arrow_try_cast.slt covering:

• Successful casts (Int64, Float64, LargeUtf8, Dictionary)
• Failed cast returning NULL
• Same-type passthrough
• NULL input
• Invalid type string errors
• Multiple casts in one query

Are there any user-facing changes?

New arrow_try_cast SQL function available.

🤖 Generated with Claude Code

[jonahgao]

LGTM, I think this is a very practical UDF.

A minor improvement might be to add more tests. The current test cases are all evaluated at compile time via constant folding. Maybe we need a test likes

select arrow_try_cast(a, 'Int64') from values('100'), (NULL), ('foo') t(a);

This would evaluate the cast during physical execution.

[adriangb]

Thanks @jonahgao !