Fix ESP32 Arduino 3.x compilation errors and Z-axis missed step pulses

[Copilot]

• Fix Serial.cpp, Spindle_PWM.cpp, AnalogOutput.cpp, Stepper.cpp, Limits.cpp — ESP32 Arduino 3.x API changes
• Fix Stepper_RMT.cpp — root cause of Z-axis incorrect movement:
  • Set RMT.apb_conf.fifo_mask = 1 in Initialize() to enable direct RMTMEM access (without this, RMTMEM writes route through the per-channel APB FIFO which is consumed on first TX, leaving nothing for subsequent steps)
  • Replace rmt_fill_tx_items with direct RMTMEM writes in Initialize()
  • Write items to RMTMEM fresh on every Step() call so data is always present regardless of FIFO state
  • Use _rmtItem[1].val = 0 (full-word zero) for the end marker
  • Add IRAM_ATTR to Step() (called from hardware timer ISR)
  • Move rmt_set_source_clk to after rmt_config

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.