Add I2C device management API with HT16K33 LED matrix support

[ralphweng2023]

Description

This PR adds a new I2C device management API for Raspberry Pi GPIO, following the existing pattern established by the ADC module. It provides a higher-level abstraction for communicating with I2C devices like LED matrices.

New Features

Core I2C Device API (raspi_i2c.h):

• open_i2c_device() - Open an I2C device by name, bus, address, and type
• i2c_write_byte(), i2c_write_register() - Write to I2C device
• i2c_read_byte(), i2c_read_register() - Read from I2C device
• close_i2c_device(), close_all_i2c_devices() - Close devices
• has_i2c_device(), i2c_device_named() - Device registry lookups

HT16K33 LED Matrix Support:

• ht16k33_init() - Initialize display (oscillator on, display on)
• ht16k33_set_brightness() - Set brightness level (0-15)
• ht16k33_clear() - Clear the display
• ht16k33_draw_pattern() - Draw an 8x8 pattern
• ht16k33_turn_off() - Turn off the display

Device Types:

• I2C_DEVICE_GENERIC - Generic I2C device
• I2C_DEVICE_HT16K33_8X8 - 8x8 LED Matrix (address 0x70)
• I2C_DEVICE_HT16K33_14SEG - 14-segment display (address 0x70)
• I2C_DEVICE_PCF8574 - I/O Expander (address 0x20)

Example Usage

#include "raspi_i2c.h"

void demo_led_matrix() {
    raspi_init();
    
    // Open the LED matrix
    i2c_device led = open_i2c_device("led_matrix", I2C_DEVICE_HT16K33_8X8);
    
    ht16k33_init(led);
    ht16k33_set_brightness(led, 8);
    
    // Draw a heart pattern
    unsigned char heart[] = {
        0b01100110, 0b11111111, 0b11111111, 0b11111111,
        0b01111110, 0b00111100, 0b00011000, 0b00000000
    };
    ht16k33_draw_pattern(led, heart);
    
    delay(2000);
    
    close_i2c_device(led);
    raspi_cleanup();
}

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Built and tested on macOS using CMake:

cd projects/cmake
cmake --preset macOS
cmake --build build/

cd ../../bin
./skunit_tests "[i2c]"
# Result: All tests passed (20 assertions in 5 test cases)

./skunit_tests --order rand  
# Result: All tests passed (1283 assertions in 84 test cases)

Testing Checklist

• Code compiles without errors on macOS
• All existing unit tests pass
• New I2C unit tests pass (5 test cases, 20 assertions)
• Null pointer handling works correctly
• Device registry functions work correctly
• Tested on Raspberry Pi with HT16K33 (requires hardware)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code in hard-to-understand areas
• My changes generate no new warnings
• I have added tests that prove my fix is effective
• New and existing unit tests pass locally with my changes