test: consolidate suites and remove redundant cases (#1459)

Regression tests were scattered across feature- and bug-specific files, and some suites repeated the same checks. Group tests by responsibility, isolate feature fixtures in test classes, and remove duplicate or obsolete cases.

The review covered all 127 collected test modules on main. This reduces them and removes or combines definitions:.

 No application code changes.

tests/test_configabc.py

@@ -10,17 +10,11 @@ Timezone contract under test:
 * When a timezone-aware datetime is supplied, ``start_time`` is
   interpreted as wall-clock time **in that timezone** — no tz
   conversion is applied to ``start_time`` itself.
-* Constructing a ``TimeWindow`` with a naive ``start_time`` raises
-  ``ValidationError``.
+* A timezone-aware ``start_time`` is normalized to a naive wall-clock time.
 """
 
 import datetime
 import json
-import os
-import sys
-
-sys.path.insert(0, os.path.dirname(__file__))
-
 from typing import cast
 
 import numpy as np
@@ -29,12 +23,9 @@ import pendulum
 import pytest
 from pydantic import ValidationError
 
-from akkudoktoreos.config.configabc import (  # noqa — ensure Time is importable
+from akkudoktoreos.config.configabc import (
     CycleTimeWindowSequence,
-)
-from akkudoktoreos.config.configabc import TimeWindow
-from akkudoktoreos.config.configabc import TimeWindow as _TW_check
-from akkudoktoreos.config.configabc import (  # noqa — ensure Time is importable
+    TimeWindow,
     TimeWindowSequence,
     ValueTimeWindow,
     ValueTimeWindowSequence,