Multiple hx711s wastes PIO/SM resources

[endail]

Each time a hx711_t is init'd, a copy of the PIO program is inserted into one of the RP2040's PIOs. It should instead:

• check if the program already exists in PIO memory
• if not, add it
• then set up an individual state machine with the program counter pointing to the program

Many SMs to one PIO.

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This will not work for hx711_multi_t.

The PIO init function modifies the PIO program itself to set the number of in pins. Individual state machines using the same PIO would therefore be required to use the same configuration.

May still be feasible for individual hx711_ts...