Fix: prevent duplicate exports by popping matched time in is_it_time_to_export

This updates `is_it_time_to_export` so that when a timestep matches a desired export time (within the `np.isclose` tolerances), the corresponding entry in `times` is popped.

Previously, multiple consecutive timesteps within the tolerance window could all trigger `True`, leading to repeated exports for the same target time, especially at high simulation times where the relative tolerance (rtol) allows larger absolute differences.

With this change:
- only the first matching timestep triggers an export
- the matched time is removed, preventing any subsequent exports for it

This ensures a 1-to-1 mapping between requested and actual exports, provided the simulation reaches timesteps sufficiently close to the target times.

Author: AdriaLlealS

src/festim/helpers.py

@@ -324,7 +324,11 @@ def is_it_time_to_export(
 ) -> bool:
     """
     Checks if the exported field should be written to a file or not based on the
-    current time and the times in `export.times`
+    current time and the times in `export.times'
+    
+    After a successful match, the corresponding time is removed from the list to
+    prevent multiple exports for the same target time.
+
 
     Args:
         current_time: the current simulation time
@@ -337,14 +341,16 @@ def is_it_time_to_export(
     """
     if times is None:
         return True
-
-    for time in times:
+    
+    for i, time in enumerate(times):
         if np.isclose(time, current_time, atol=atol, rtol=rtol):
+            times.pop(i)  # consume the time so it is not exported again
             return True
 
     return False
 
 
+
 _residual0 = 0
 _prev_xnorm = 0