Add explicit bytes conversion with {bytes, Binary} tuple

[benoitc]

Summary

• Add support for {bytes, Binary} tagged tuple to explicitly convert Erlang binaries to Python bytes
• By default, binaries are UTF-8 decoded to str; this provides explicit control
• Useful for binary protocols, images, and compressed data

Usage

%% Default: binary -> str
py:call(mod, func, [<<"hello">>])  %% Python receives: "hello" (str)

%% Explicit: {bytes, binary} -> bytes  
py:call(mod, func, [{bytes, <<"hello">>}])  %% Python receives: b"hello" (bytes)