Disable MustBe in the code

[rmolinari]

In rpeg.rb we have a call to MustBe.disable.

When this call is made I get a bunch of warnings:

/Users/rory/.rvm/gems/ruby-3.1.0/gems/must_be-1.1.0/lib/must_be/core.rb:45: warning: method redefined; discarding old must_never_ever_contain
/Users/rory/.rvm/gems/ruby-3.1.0/gems/must_be-1.1.0/lib/must_be/containers.rb:293: warning: previous definition of must_never_ever_contain was here
/Users/rory/.rvm/gems/ruby-3.1.0/gems/must_be-1.1.0/lib/must_be/core.rb:45: warning: method redefined; discarding old must_not_be
/Users/rory/.rvm/gems/ruby-3.1.0/gems/must_be-1.1.0/lib/must_be/basic.rb:14: warning: previous definition of must_not_be was here
[many more]

Work out why and fix the problem.