Add support for PCF8575 I/O expander

[dclause]

Motivation:
The PCF8575 is a widely used 16-bit I²C I/O expander, commonly found in embedded systems.
Adding support for this device would extend compatibility for I/O expansion over I²C and benefit users needing more digital I/Os.

Scope:

• Implement an expander for the PCF8575
• Support input and output modes
• Expose a consistent API with existing expanders
• Consider exposing low-level utilities (e.g., bit-shifting helpers)

Impact:
New feature: no impact on existing functionality.