perf(interval_pool): hoist fetch_groups and precompute period criteria

- Move UTC import from inline (inside _has_real_gaps_in_range) to
  module-level in manager.py
- Hoist get_fetch_groups() out of while loop in _get_cached_intervals:
  eliminates ~384 function calls per invocation
- Pre-compute criteria_by_day dict in build_periods before the for-loop:
  eliminates ~381 redundant NamedTuple constructions per call; only
  ref_price/avg_price vary by day (max 3 entries), flex/min_distance/
  reverse_sort are constant throughout

Impact: Reduces unnecessary object creation during the hot paths called
every 15 minutes and during all relaxation phases.

custom_components/tibber_prices/coordinator/period_handlers/period_building.py

@@ -112,6 +112,19 @@ def build_periods(  # noqa: PLR0913, PLR0915, PLR0912 - Complex period building
     intervals_filtered_by_flex = 0
     intervals_filtered_by_min_distance = 0
 
+    # Pre-compute criteria per day (flex/min_distance/reverse_sort are constant throughout;
+    # only ref_price and avg_price vary by day — max 3 entries: yesterday/today/tomorrow)
+    criteria_by_day: dict[date, TibberPricesIntervalCriteria] = {
+        day: TibberPricesIntervalCriteria(
+            ref_price=ref_prices[day],
+            avg_price=avg_prices[day],
+            flex=flex,
+            min_distance_from_avg=min_distance_from_avg,
+            reverse_sort=reverse_sort,
+        )
+        for day in ref_prices
+    }
+
     for price_data in all_prices:
         starts_at = time.get_interval_time(price_data)
         if starts_at is None:
@@ -133,13 +146,7 @@ def build_periods(  # noqa: PLR0913, PLR0915, PLR0912 - Complex period building
         ref_date = date_key
 
         # Check flex and minimum distance criteria (using smoothed price and interval's own day reference)
-        criteria = TibberPricesIntervalCriteria(
-            ref_price=ref_prices[ref_date],
-            avg_price=avg_prices[ref_date],
-            flex=flex,
-            min_distance_from_avg=min_distance_from_avg,
-            reverse_sort=reverse_sort,
-        )
+        criteria = criteria_by_day[ref_date]
         in_flex, meets_min_distance = check_interval_criteria(price_for_criteria, criteria)
 
         # Track why intervals are filtered

custom_components/tibber_prices/interval_pool/manager.py

@@ -5,7 +5,7 @@ from __future__ import annotations
 import asyncio
 import contextlib
 import logging
-from datetime import datetime, timedelta
+from datetime import UTC, datetime, timedelta
 from typing import TYPE_CHECKING, Any
 from zoneinfo import ZoneInfo
 
@@ -459,8 +459,6 @@ class TibberPricesIntervalPool:
             True if a real gap exists, False if the range is fully covered.
 
         """
-        from datetime import UTC  # noqa: PLC0415 - UTC constant needed here only
-
         cached_intervals = self._get_cached_intervals(start_iso, end_iso)
 
         if not cached_intervals:
@@ -582,14 +580,13 @@ class TibberPricesIntervalPool:
         resolution_change_naive = datetime(2025, 10, 1)  # noqa: DTZ001
         interval_minutes = INTERVAL_QUARTER_HOURLY if current_naive >= resolution_change_naive else INTERVAL_HOURLY
 
+        fetch_groups = self._cache.get_fetch_groups()
         while current_naive < end_naive:
             # Check if this timestamp exists in index (O(1) lookup)
             current_dt_key = current_naive.isoformat()[:19]
             location = self._index.get(current_dt_key)
 
             if location is not None:
-                # Get interval from fetch group
-                fetch_groups = self._cache.get_fetch_groups()
                 fetch_group = fetch_groups[location["fetch_group_index"]]
                 interval = fetch_group["intervals"][location["interval_index"]]
                 # CRITICAL: Return shallow copy to prevent external mutations