feat: add cast_to_type UDF for type-based casting

[adriangb]

Which issue does this PR close?

N/A — new feature

Rationale for this change

DuckDB provides a cast_to_type(expression, reference) function that casts the first argument to the data type of the second argument. This is useful in macros and generic SQL where types need to be preserved or matched dynamically. This PR adds the equivalent function to DataFusion, along with a fallible try_cast_to_type variant.

What changes are included in this PR?

• New cast_to_type scalar UDF in datafusion/functions/src/core/cast_to_type.rs
  • Takes two arguments: the expression to cast, and a reference expression whose type (not value) determines the target cast type
  • Uses return_field_from_args to infer return type from the second argument's data type
  • simplify() rewrites to Expr::Cast (or no-op if types match), so there is zero runtime overhead
• New try_cast_to_type scalar UDF in datafusion/functions/src/core/try_cast_to_type.rs
  • Same as cast_to_type but returns NULL on cast failure instead of erroring
  • simplify() rewrites to Expr::TryCast
  • Output is always nullable
• Registration of both functions in datafusion/functions/src/core/mod.rs

Are these changes tested?

Yes. New sqllogictest file cast_to_type.slt covering both functions:

• Basic casts (string→int, string→double, int→string, int→double)
• NULL handling
• Same-type no-op
• CASE expression as first argument
• Arithmetic expression as first argument
• Nested calls
• Subquery as second argument
• Column references as second argument
• Boolean and date casts
• Error on invalid cast (cast_to_type) vs NULL on invalid cast (try_cast_to_type)
• Cross-column type matching

Are there any user-facing changes?

Two new SQL functions:

• cast_to_type(expression, reference) — casts expression to the type of reference
• try_cast_to_type(expression, reference) — same, but returns NULL on failure

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