fix: clamp lag parameter to buffer size with warning (fixes #379)

The circular buffer in plotymlag.py has a fixed size of 10. When a user
sets lag >= size via tryparam, the modulo arithmetic silently wraps,
producing incorrect data (e.g., lag=15 behaves like lag=5).

Add input validation that clamps lag to size-1 and emits a
logging.warning when the requested value exceeds the buffer capacity.
This prevents silent data corruption while preserving backward
compatibility and the existing circular buffer logic.

Author: GaneshPatil7517

tools/plotymlag.py

@@ -2,9 +2,16 @@
 import numpy as np
 import matplotlib.pyplot as plt
 import time
+import logging
 
 size = 10
-lag = concore.tryparam("lag", 0) 
+lag = concore.tryparam("lag", 0)
+if lag >= size:
+    logging.warning(
+        "Requested lag (%d) exceeds buffer size (%d). Clamping to %d.",
+        lag, size, size - 1
+    )
+    lag = size - 1
 print("plot ym with lag="+str(lag))
 
 concore.delay = 0.005