Start Seeed XIAO RP2040 on PlatformIO

#include <Arduino.h>
#include <Adafruit_NeoPixel.h>

const int pin_0 = 0;
const int pin_1 = 1;
const int pin_2 = 2;
const int pin_3 = 3;
const int pin_4 = 4;
const int pin_6 = 6;
const int pin_7 = 7;
const int pin_26 = 26;
const int pin_27 = 27;
const int pin_28 = 28;
const int pin_29 = 29;

const int user_led_green = 16;
const int user_led_red   = 17;
const int user_led_blue  = 25;

const int rgb_power_pin  = 11;
const int rgb_data_pin   = 12;

constexpr int num_of_pins = 16;
int all_pins[num_of_pins] = {
  pin_0,
  pin_1,
  pin_2,
  pin_3,
  pin_4,
  pin_6,
  pin_7,
  pin_26,
  pin_27,
  pin_28,
  pin_29,
  user_led_green,
  user_led_red,
  user_led_blue,
  rgb_power_pin,
  rgb_data_pin
};

constexpr int NUM_RGB_COLORS = 5;
int rgb_colors[NUM_RGB_COLORS][3] = {
  {254,10,10},
  {10,254,10},
  {10,10,254},
  {254,254,10},
  {10,254,254}
};

// https://learn.microsoft.com/en-us/cpp/cpp/constexpr-cpp?view=msvc-170&viewFallbackFrom=vs-2019
constexpr int RGB_PIXELS = 1;

constexpr int DELAY_TIME = 500;

Adafruit_NeoPixel pixels(RGB_PIXELS, rgb_data_pin, NEO_GRB + NEO_KHZ800);

void setup() {
  Serial.begin(115200);

  for (int i = 0; i < num_of_pins; i++){
    pinMode(all_pins[i], OUTPUT);
  }

  digitalWrite(rgb_power_pin, HIGH); // RGB Power ON

  pixels.begin();
}

void loop() {

  // Pins test
  for (size_t i = 0; i < (num_of_pins-2); i++){
    digitalWrite(all_pins[i], HIGH);
    delay(DELAY_TIME);
    digitalWrite(all_pins[i], LOW);
    delay(DELAY_TIME);
  }

  // RGB LED test
  for (size_t i = 0; i < NUM_RGB_COLORS; i++){
    pixels.clear();
    pixels.setPixelColor(0, pixels.Color(rgb_colors[i][0], rgb_colors[i][1], rgb_colors[i][2]));
    pixels.show();
    delay(DELAY_TIME);
  }
  pixels.clear();
  pixels.setPixelColor(0, pixels.Color(0,0,0));
  pixels.show();
}