Turn CH32V003 into I2C port expander

Features:

• act as I2C slave
• configurable own I2C address
• convert other pins into GPIO ports
• receive GPIO commands from I2C master
• configurable physical to logical port remapping
• ADC? SPI? UART? ...
• interrupt pin?
• emulate standard I2C expander chips

I2C expander chips

• https://www.nxp.com/docs/en/data-sheet/PCF8575.pdf
• https://cdn-shop.adafruit.com/datasheets/mcp23017.pdf
• https://www.ti.com/lit/ds/symlink/tcal9539.pdf
• https://www.ti.com/lit/ds/symlink/tca9554.pdf
• https://www.ti.com/lit/ds/symlink/tcal6416r.pdf
• https://www.ti.com/interface/i2c/general-purpose-ios-gpios/products.html