feat: encoding fallback strategy

~~Hi, I saw there is a fallback strategy for encoding in the fork of this repo
[Fix decoding encodage](https://github.com/joliverapolyconseil/python-oxmsg/commit/476d8fc96347799df4aefd880b2957463cb38407) from @joliverapolyconseil
It may be better with some version of Outlook.~~

Hi,

Some encoding is system aware

Thanks