Add alias and predicate support

[bnlucas]

This adds attribute aliasing and predicate support to both class- and instance-level attributes.

Alias Support

Defines an alias method that is not registered on the class context, just a simple proxy to the original method. An error is raised if the method you're trying to alias has not been defined.

class Config
  cattr :enabled, default: true     # iattr :enabled, default: true
  cattr_alias :allowed, :enabled    # iattr_alias :allowed, :enabled

  cattr_alias :alias_attr, :unknown # raises Cattri::AttributeNotDefinedError

  # Config.allowed -> def allowed; send(:enabled); end
end

Predicate support

The new predicate: true|false flag on cattr ... and iattr ... defines a proxy method of #{name}? that is not registered on the class context. This proxy calls !!send(:name).

A guard was also added in so attributes cannot be defined as predicates directly, they must use the new flag on a regular attribute.

class Config
  cattr :enabled?                                   # raises Cattri::AttributeError
  cattr :enabled, default: true, predicate: true    # iattr :enabled, default: true, predicate: true

  # Config.enabled? -> def enabled?; !!send(:enabled); end
end

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (23f5b6e) to head (cae7ea7).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main        #4   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            9         9           
  Lines          311       343   +32     
  Branches        34        44   +10     
=========================================
+ Hits           311       343   +32     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.