perf: Expand reflected calls into Client methods

[kattrali]

Goal

Improve performance and shrink callstacks by removing the reflection calls from Client to Configuration. Also beef up test coverage for config options!

Related to #476

Changeset

Removed the __call method from Client, replacing it with the instance methods from Configuration.

Tests

Added new unit tests for the return values and behaviors of Client to ensure that:

• The setters which return the instance still return the right thing
• The getters return the same object as before

The tests pass before and after the change.

[Cawllec]

Looks good: Checked all the methods have been covered, tests cover everything, and it works in a Laravel test application.