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_i2c_xiao-ble.go

@@ -0,0 +1,38 @@
+//go:build xiao_ble
+
+// This initializes SSD1306 OLED display driver over I2C.
+//
+// Seeed XIAO BLE board + SSD1306 128x32 I2C OLED display.
+//
+// Wiring:
+// - XIAO GND      -> OLED GND
+// - XIAO 3v3      -> OLED VCC
+// - XIAO D4 (SDA) -> OLED SDA
+// - XIAO D5 (SCL) -> OLED SCK
+//
+// For your case:
+// - Connect the display to I2C pins on your board.
+// - Adjust I2C address and display size as needed.
+
+package main
+
+import (
+	"machine"
+
+	"tinygo.org/x/drivers/ssd1306"
+)
+
+func newSSD1306Display() *ssd1306.Device {
+	machine.I2C0.Configure(machine.I2CConfig{
+		Frequency: 400 * machine.KHz,
+		SDA:       machine.SDA0_PIN,
+		SCL:       machine.SCL0_PIN,
+	})
+	display := ssd1306.NewI2C(machine.I2C0)
+	display.Configure(ssd1306.Config{
+		Address: ssd1306.Address_128_32, // or ssd1306.Address
+		Width:   128,
+		Height:  32, // or 64
+	})
+	return display
+}