[SPARK-52428] Harden miscellaneous module error handling

[rafafrdz]

Summary

• types.rs: Change from_str_name() to return Result<DataType, SparkError>, replace interval unimplemented!() with safe fallbacks
• storage.rs: Replace unimplemented!() with StorageLevel::None default
• catalog.rs: Replace unimplemented!() with Err(SparkError::NotYetImplemented(...))
• conf.rs: Replace .first().unwrap() with .ok_or_else()
• plan.rs: Improve panic message, eliminate unwrap via pattern matching
• functions/mod.rs: Replace unimplemented!() with todo!() in dead-code functions

Test plan

• cargo build passes
• cargo test unit tests pass
• cargo fmt -- --check passes