pin and irq operations affect the entire pio block. with pins this is
not very problematic since pins themselves are resources, but irqs are
not treated like that and can thus interfere across state machines. the
ability to wait for an irq on a state machine is kept to make
synchronization with user code easier, and since we can't inspect loaded
programs at build time we wouldn't gain much from disallowing waits from
state machines anyway.
This example also uses a pio program compiled at runtime, rather than one built at compile time. There's no reason to do that, but it's probably useful to have an example that does this as well.
