fix: use str2time() instead of datetime.fromisoformat() in is_running() and load_plan()

datetime.fromisoformat() on Python 3.9/3.10 rejects ISO strings with
colon-less UTC offsets (e.g. '+0100'), which raises ValueError inside
is_running() and reports a false unhealthy status, and drops the saved
plan in load_plan(). str2time() in utils.py already parses these formats
across Python versions via a strptime fallback.

Also widens the is_running() except clause to (ValueError, TypeError)
to match load_plan().

Fixes #5181

Author: headbouyJB

apps/predbat/predbat.py

@@ -77,6 +77,7 @@
 from config import APPS_SCHEMA, CONFIG_ITEMS
 import debug_history
 from utils import (
+    str2time,
     minutes_since_yesterday,
     minutes_since_midnight,
     dp1,
@@ -843,7 +844,7 @@ def load_plan(self):
             return
 
         try:
-            saved_dt = datetime.fromisoformat(saved_updated)
+            saved_dt = str2time(saved_updated)
         except (ValueError, TypeError):
             self.log("Warning: Saved plan timestamp is invalid, ignoring")
             return
@@ -1984,8 +1985,8 @@ def is_running(self):
             return False
 
         try:
-            predbat_last_updated = datetime.fromisoformat(predbat_last_updated)
-        except ValueError:
+            predbat_last_updated = str2time(predbat_last_updated)
+        except (ValueError, TypeError):
             return False
 
         # Check if the last updated time is within the last 15 minutes. An install upgraded