feat: Implement Type Casting and toString for Literals

[HeartLinked]

• Implements the complete type casting logic for iceberg::Literal in the LiteralCaster class to align with the Java reference implementation. This is critical for expression evaluation and predicate pushdown.
• Add basic implementation for fixed type.
• Updated ToString() to match Java's output format for better consistency (e.g., X'...' for binary).
• Added comprehensive unit tests to validate all new casting logic and ToString() formatting.

[wgtmac]

I think these switch cases can be easily rewritten by return std::to_string(std::get<typename LiteralTraits<type_id>::ValueType>(value_)); once #185 is merged.