feat: ✨ Make controller ctor constexpr

[ion098]

Summary:

Changes the pros::Controller constructor to be constexpr.

Motivation:

Allows pros::Controller instances to be declared constinit/constexpr.

Test Plan:

• Check it compiles
• Check that Controller instances can be declared as constinit/constexpr.

[BennyBot]

/azp run

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Azure Pipelines successfully started running 1 pipeline(s).

[djava]

While you're doing this, what other ctors should this be applied to? I imagine this isn't the only one.

[ion098]

While you're doing this, what other ctors should this be applied to? I imagine this isn't the only one.

The issue is that some device ctors can't be made constexpr becuase they touch global state (changing this would require a breaking change to the PROS API which I don't think is gonna happen now), it feels a bit weird to have some devices with constexpr ctors and others without.