fix: address Copilot review on #4644 - kwh precision in split slots

dp2() on both sides of the cap-boundary split let low_kwh + high_kwh
drift from the original kwh via double-rounding, and made the split
path's kwh precision inconsistent with this function's non-split
chunks, which already carry full-precision kwh (dp2() only applied to
cost/soc downstream). Kept full precision for the split kwh values
instead, matching the rest of the function.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: chalfontchubby

apps/predbat/octopus.py

@@ -2666,12 +2666,15 @@ def load_octopus_slots(self, car_n, octopus_slots, octopus_intelligent_consider_
                 elif available_blocks <= 0:
                     chunks = [(start_minutes, end_minutes, kwh, self.rate_max_base)]
                 else:
+                    # Full precision here - rounding to dp2() on both sides can make low_kwh + high_kwh
+                    # drift from the original kwh, and this function's non-split chunks already carry
+                    # kwh at full precision too (dp2() is only applied downstream, to cost/soc).
                     split_minute = min(slot_block_start + available_blocks * 30, end_minutes)
                     span = end_minutes - start_minutes
-                    low_kwh = dp2(kwh * (split_minute - start_minutes) / span) if span > 0 else 0.0
+                    low_kwh = kwh * (split_minute - start_minutes) / span if span > 0 else 0.0
                     chunks = [
                         (start_minutes, split_minute, low_kwh, self.rate_min_base),
-                        (split_minute, end_minutes, dp2(kwh - low_kwh), self.rate_max_base),
+                        (split_minute, end_minutes, kwh - low_kwh, self.rate_max_base),
                     ]
 
             for chunk_start, chunk_end, chunk_kwh, slot_average in chunks:

apps/predbat/tests/test_octopus_slots.py

@@ -120,8 +120,9 @@ def run_load_octopus_slots_tests(my_predbat):
             # flipping to the max rate (batpred#4624).
             slot_block_start = (minutes_start // 30) * 30
             split_minute = slot_block_start + 2 * 30  # 2 blocks (12 - 10) remain in the daily budget
-            low_kwh = dp2(5.0 * (split_minute - minutes_start) / 60)
-            high_kwh = dp2(5.0 - low_kwh)
+            # Full precision to match production - only cost is rounded (batpred#4644 review).
+            low_kwh = 5.0 * (split_minute - minutes_start) / 60
+            high_kwh = 5.0 - low_kwh
             for target in (expected_slots5, expected_slots8):
                 target.append({"start": minutes_start, "end": split_minute, "kwh": low_kwh, "average": 4, "cost": dp2(4 * low_kwh), "soc": 10, "octopus": True})
                 target.append({"start": split_minute, "end": minutes_end, "kwh": high_kwh, "average": 10, "cost": dp2(10 * high_kwh), "soc": 10, "octopus": True})