add invert rectangle function

[kossnikita]

Inverts the color of pixels in rectangle. Useful for progress bar and menu selection.

An optimized algorithm used instead of inverting each pixel by coordinate.

SSD1306_Error_t ssd1306_InvertRectangle(uint8_t x1, uint8_t y1, uint8_t x2, uint8_t y2);

[afiskon]

Looks good. Please add a call of the new function to ssd1306_TestAll().

[kossnikita]

Added tests

[afiskon]

👍