Function code_to_column_base 

pub fn code_to_column_base(code: &str) -> String

Converts a SearchParameter code into a safe PostgreSQL column base name: lowercased, with every character outside [a-z0-9_] folded to _.

FHIR codes are already restricted to a conservative character set, but _lastUpdated (leading underscore, camelCase) and hyphenated codes like address-city both need normalizing.