Moves claiming of sm to init; destructor frees pio resources.

[MarcusGarfunkel]

• Describe the scope of your change--i.e. what the change does and what parts of the code were modified. This will help us understand any risks of integrating the code. I've moved the claiming of a pio state machine from the constructor to the rp2040Init function. I've added the necessary unclaiming sm functions to the destructor, dependent on whether the init function had been called.

• Describe any known limitations with your change. For example if the change doesn't apply to a supported platform of the library please mention it. No know limitations.

• Please run any tests or examples that can exercise your modified code. We strive to not break users of the code and running tests/examples helps with this process. I've tested this myself, but I'd recommend testing with your examples.