function createStreamManagerWriter
Swift
func createStreamManagerWriter<T>(streamManager: UnsafeMutableRawPointer, streamId: UInt64, initialPayloadCapacity: Int, initialCredits: UInt32 = 0, serializer: @escaping (FlatBuffer, Int, T) -> Void) -> NPRPCStreamWriter<T> where T : Sendable
A writer for stream streamId on a session's stream manager, starting
with the consumer's advertised initialCredits. Used by generated code.
nprpc_swift/Sources/NPRPC/StreamReader.swift:650