Mark pyclasses frozen if possible. #1250

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
Related to #1248
If pyclasses have &mut self then they can't be used by python threading.
Many classes in the repo are thin wrappers around rust structs which already manage concurrency.
This should reduce Already Borrowed errors and shouldn't change any functionality in many cases.
For more complex wrappers this might be more challenging or not possible.

Describe the solution you'd like
Mark classes as frozen, remove mut self confirm if things still compile and tests pass.