Add requiredParameterCount to SymbolDefinition and MethodSignature,
enabling range-based arity filtering in filterCallableCandidates.
Calls with omitted optional/default arguments now resolve correctly.
Supported: TS, Python, Kotlin, C#, C++, PHP, Ruby (7 languages).
Detection via OPTIONAL_PARAM_TYPES set + hasDefaultValue helper.
9 integration tests added across all 7 languages.