Portable SSD1306 OLED driver for STM32 using STM32Cube HAL, with pluggable I2C/SPI transport callbacks.

• Transport-agnostic architecture (I2C and SPI)
• No hard dependency on a specific STM32 peripheral instance
• Config-driven display setup through OLED_Config
• Built-in SSD1306 initialization sequence
• Full-screen operations (OLED_Clear, OLED_Fill, OLED_DrawBitmap)
• Partial updates via OLED_DrawBitmapRect and OLED_SetAddressWindow
• Display control APIs:
  • OLED_DisplayOn
  • OLED_SetInvert
  • OLED_SetEntireDisplayOn
  • OLED_SetContrast
• Graphics adapter (OLED_GfxFlushCallback) for external framebuffer pipelines

• include/ssd1306.h: public API
• src/ssd1306.c: driver implementation
• examples/base_init_i2c.c: I2C transport example
• examples/base_init_spi.c: SPI transport example
• examples/draw_bitmap_i2c.c: I2C bitmap rendering example
• examples/display_controls_i2c.c: display control API example
• examples/partial_update_i2c.c: partial update example
• src/main.c: local demo with controls + animated partial updates
• documentation.md: detailed API/usage documentation

1. Configure your STM32 clock/GPIO/bus peripheral (I2C or SPI).
2. Implement a transport callback (OLED_SendI2CFn or OLED_SendSPIFn).
3. Fill OLED_Config with display size and callback.
4. Call OLED_Init(&oled).
5. Render using OLED_Clear, OLED_Fill, OLED_DrawBitmap, or OLED_DrawBitmapRect.
6. Use control APIs (OLED_SetInvert, OLED_SetContrast, OLED_DisplayOn) as needed.

OLED_Config oled = {
    .bus_type = OLED_BUS_I2C,
    .width = 128U,
    .height = 64U,
    .user_context = &hi2c,
    .transport = {
        .i2c = {
            .i2c_address_7bit = 0x3CU,
            .send_fn = oled_send_i2c
        }
    }
};

if (OLED_Init(&oled) != OLED_OK) {
    Error_Handler();
}
OLED_Fill(&oled, 0x00U);

OLED_Config oled = {
    .bus_type = OLED_BUS_SPI,
    .width = 128U,
    .height = 64U,
    .user_context = &hspi,
    .transport = {
        .spi = {
            .send_fn = oled_send_spi
        }
    }
};

• OLED_OK: success
• OLED_ERR_INVALID_ARG: bad arguments/config
• OLED_ERR_IO: bus transfer failure

• For I2C, use SSD1306 7-bit address (0x3C is common).
• For SPI, your callback should drive D/C (command/data select) and optionally CS.
• OLED_DrawBitmap requires a full framebuffer of exactly OLED_BufferSize(cfg) bytes.
• OLED_DrawBitmapRect length must match rectangle bytes: (column_end - column_start + 1) * (page_end - page_start + 1).

See documentation.md for complete API details.