ssd1306: avoid unnecessary heap allocations (#767)

* ssd1306: avoid unnecessary heap allocations

* ssd1306: extract i2c and spi bus implementations

* ssd1306: refactor tests -- show fps and heap usage

* ssd1306: bring back the lost exported methods

* Adjust examples

* Fix smoketests for ssd1306

examples/ssd1306/main_spi_xiao-rp2040.go

@@ -0,0 +1,40 @@
+//go:build xiao_rp2040
+
+// This initializes SSD1306 OLED display driver over SPI.
+//
+// Seeed XIAO RP2040 board + SSD1306 128x64 SPI OLED display.
+//
+// Wiring:
+// - XIAO GND       -> OLED GND
+// - XIAO 3v3       -> OLED VCC
+// - XIAO D8 (SCK)  -> OLED D0
+// - XIAO D10 (SDO) -> OLED D1
+// - XIAO D4        -> OLED RES
+// - XIAO D5        -> OLED DC
+// - XIAO D6        -> OLED CS
+//
+// For your case:
+// - Connect the display to SPI pins on your board.
+// - Adjust RES, DC and CS pins as needed.
+// - Adjust SPI frequency as needed.
+// - Adjust display size as needed.
+
+package main
+
+import (
+	"machine"
+
+	"tinygo.org/x/drivers/ssd1306"
+)
+
+func newSSD1306Display() *ssd1306.Device {
+	machine.SPI0.Configure(machine.SPIConfig{
+		Frequency: 50 * machine.MHz,
+	})
+	display := ssd1306.NewSPI(machine.SPI0, machine.D5, machine.D4, machine.D6)
+	display.Configure(ssd1306.Config{
+		Width:  128,
+		Height: 64,
+	})
+	return display
+}