Fix Python wrapper doc namespace rendering

[MukundaKatta]

Closes #500

Summary

• remove the extra namespace separator from the Python wrapper class doc template
• update checked-in generated wrapper docs from mx::::Type to mx::Type

Verification

• rg -n "mx::::|Wrapper for \{cxx_namespace\}::\{cxx_class_name\}" bin/Bootstrap/PythonBindings.py bindings/Python || true
• python3 -m py_compile bin/Bootstrap/PythonBindings.py
• git diff --check

I did not run a full C++ build locally because this is a generated doc-string only change across many checked-in wrapper files.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}