Refactor n_chase pattern for bidirectional movement

- Updated n_chase to support bidirectional movement with n3 and n4 parameters
- n3 controls forward steps per direction change
- n4 controls backward steps per direction change
- Pattern alternates between moving forward n3 steps and backward n4 steps
- Each direction repeats for the specified number of steps before switching
- Added test/9.py with n1=20, n2=20, n3=20, n4=-5 parameters
- Updated to run as a thread-based pattern similar to other patterns

test/n_chase/9.py

@@ -0,0 +1,62 @@
+#!/usr/bin/env python3
+"""
+N-chase test 9: Cyan, on=20, off=20, delay=200ms
+Runs forever
+Run with: mpremote run test/n_chase/9.py
+"""
+
+import patterns
+import utime
+from settings import Settings
+from machine import WDT
+
+print("Starting N-Chase Test 9: Cyan, on=20, off=20, delay=200ms")
+print("Press Ctrl+C to stop")
+
+# Load settings
+settings = Settings()
+
+# Initialize patterns using settings
+p = patterns.Patterns(
+    pin=settings["led_pin"], 
+    num_leds=settings["num_leds"], 
+    brightness=255,
+    delay=200
+)
+
+# Configure test parameters
+p.n1 = 20   # On width 20
+p.n2 = 20   # Off width 20
+p.n3 = 20   # Reserved for future use
+p.n4 = -5   # Reserved for future use
+p.colors = [(0, 255, 255)]  # Cyan
+
+print(f"LED Pin: {settings['led_pin']}")
+print(f"LEDs: {settings['num_leds']}")
+print(f"Brightness: {p.brightness}")
+print(f"Delay: {p.delay}ms")
+print(f"On width: {p.n1}")
+print(f"Off width: {p.n2}")
+print(f"n3: {p.n3}")
+print(f"n4: {p.n4}")
+print(f"Color: {p.colors[0]}")
+
+# Initialize watchdog timer
+wdt = WDT(timeout=10000)
+wdt.feed()
+
+# Start pattern
+p.select("nc")
+print("Pattern started. Running forever...")
+
+# Run forever
+try:
+    while True:
+        wdt.feed()
+        utime.sleep_ms(100)
+except KeyboardInterrupt:
+    print("\nStopping...")
+    p.run = False
+    p.off()
+    print("LEDs turned off")
+