feat: extend PinMode enum with INPUT_FLOATING and INPUT_ANALOG

[Aymane-ST]

Summary

Extend PinMode with:

• INPUT_FLOATING = INPUT
• INPUT_ANALOG = 0x5

Also add:

• OUTPUT_OPEN_DRAIN = OUTPUT_OPENDRAIN

Why

Some cores, especially STM32, expose more explicit GPIO modes than the current common API:

• INPUT_FLOATING improves readability and compatibility with existing code, while remaining an alias of INPUT
• INPUT_ANALOG exposes a real hardware mode available on many MCUs
• OUTPUT_OPEN_DRAIN provides a clearer alias for the existing spelling

Compatibility

This is backward-compatible:

• existing values are unchanged
• aliases do not change behavior
• INPUT_ANALOG is additive and only affects code that explicitly uses it

Benefit

This makes the generic API more expressive and reduces the need for core-specific pin mode constants in sketches and libraries.