SPI: Add half-duplex support

[outlandnish]

Summary

This PR fixes/implements the following bugs/features

• [x] Feature: Implement conditional GPIO configuration based on device mode and duplex setting
• [x] Breaking changes: begin and beginTransaction now return a boolean indicating if they succeeded
• [x] Breaking changes: spi_transfer_e returns a spi_status_e instead of void

Validation

• [TODO]: Demonstrate the code is solid. [e.g. Provide a sketch]