feat: add structured UDT literal support with dual encoding

[benbellick]

This is build on top of #613, so I'll only open it up for proper review once that is merged in.

Closes #612

[benbellick]

• Substrait allows two encodings for UDT literals: Any (opaque bytes) and struct (typed fields). Calcite has no native UDT literal, so we need Calcite-side carriers that preserve both the payload and the UDT type.

• Existing pattern for Any: we already used REINTERPRET over a binary literal to shuttle UserDefinedAnyLiteral payloads. We kept that because it’s minimal and reuses Calcite’s reinterpret machinery without new operators.

• Struct-encoded UDTs: Calcite’s natural literal for structured payloads is ROW(...). To keep the UDT type, we wrap the ROW in a REINTERPRET cast to the UDT type, mirroring the Any path: payload literal + reinterpret to UDT.

• Reverse path (Calcite → Substrait): peel the REINTERPRET; if the operand is binary, rebuild UserDefinedAnyLiteral; if it’s ROW, rebuild UserDefinedStructLiteral. A general ROW converter was added so struct literals can be reconstructed for reinterpret.

• Why this shape: it gives a uniform pattern—outer type is always the UDT via reinterpret; inner literal is the chosen encoding (binary or ROW). It keeps Calcite changes small, leverages existing operators, and aligns with Substrait’s dual-encoding spec.