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_elecpriceenergycharts.py

@@ -1,4 +1,3 @@
-import asyncio
 import json
 from collections.abc import Callable
 from pathlib import Path
@@ -8,16 +7,10 @@ import numpy as np
 import pandas as pd
 import pytest
 import requests
-from loguru import logger
 
 from akkudoktoreos.core.cache import CacheFileStore
 from akkudoktoreos.core.coreabc import get_ems
 from akkudoktoreos.prediction.elecfeefixed import ElecFeeFixed
-from akkudoktoreos.prediction.elecpriceakkudoktor import (
-    AkkudoktorElecPrice,
-    AkkudoktorElecPriceValue,
-    ElecPriceAkkudoktor,
-)
 from akkudoktoreos.prediction.elecpriceenergycharts import (
     ElecPriceEnergyCharts,
     EnergyChartsElecPrice,