Ensure any fields that could intersect with Message are renamed

[Gobot1234]

Follows from a conversation with @danielgtaylor. THIS IS A BREAKING CHANGE

parse -> parse_ serialized_on_wire -> serialized_on_wire_ foo -> foo

This allows us to reserve names for betterproto. I'll need to document this somewhere.

[cetanu]

Which part of this is breaking? The change overall seems fine to me.

[Gobot1234]

I removed the which_one_of and serialised_on_wire methods

[cetanu]

I see... and they are attributes on the messages instead... That seems like good value in my opinion