container.*: fix stubtest errors - #2454

av.container.core.Chapter is not present at runtime
av.container.core.Container is a disjoint base at runtime, but isn't marked with @disjoint_base in the stub
av.container.core.Real is not present at runtime

av.container.input.InputContainer cannot be subclassed at runtime, but isn't marked with @final in the stub

av.container.output.OutputContainer cannot be subclassed at runtime, but isn't marked with @final in the stub
av.container.output.OutputContainer is a disjoint base at runtime, but isn't marked with @disjoint_base in the stub

av.container.streams.StreamContainer cannot be subclassed at runtime, but isn't marked with @final in the stub
av.container.streams.StreamContainer is a disjoint base at runtime, but isn't marked with @disjoint_base in the stub
av.container.streams.StreamContainer.__getitem__ is inconsistent, stub parameter "index" should be positional-only (add "/", e.g. "key, /")