Refactor rainbow pattern to travel along the length of LED strip

- Modified rainbow() to distribute colors along the physical length
- Each LED gets a different hue based on its position
- n1 parameter controls how many times the rainbow cycles (nodes)
- Split rainbow tests into test/rainbow/ directory with 9 numbered test files
- Each test runs forever until interrupted
- Added main.py to run all tests in sequence repeatedly

patterns.py

@@ -117,8 +117,11 @@ class Patterns(PatternBase): # Inherit from PatternBase
                 pos -= 170
                 return (0, pos * 3, 255 - pos * 3)
 
+        # Rainbow travels along the length - each LED position gets a different color
         for i in range(self.num_leds):
-            rc_index = (i * 256 // self.num_leds) + self.pattern_step
+            # Map LED position along strip to rainbow color
+            # Full 256 color range distributed along the strip length
+            rc_index = ((i * 256 // self.num_leds) + self.pattern_step) % 256
             self.n[i] = self.apply_brightness(wheel(rc_index & 255))
         self.n.write()
         self.pattern_step = (self.pattern_step + 1) % 256