perf: import heavy optional dependencies on first use (#1377)

A GENETIC server with external (import) providers and EOSdash disabled
loads several large packages at start that it never uses, which costs
a noticeable part of the memory on 512 MB boards:

- matplotlib via the GENETIC/GENETIC0 PDF report modules (server/eos.py)
- statsmodels via the Holt-Winters fallback in prediction/priceabc.py
- pvlib via the weather base class and the pvlib-based providers
- bs4/lxml via the ClearOutside provider
- scipy via the self-consumption interpolator singletons, which were
  loaded at import time
- the GENETIC0 optimizer, imported by core/ems.py
- tzfpy, whose polygon data the computed general.timezone loads

Import these where they are used. The interpolator tables are loaded
on first use (thread-safe). Nothing changes in what is computed.

general.timezone is computed from latitude/longitude and cannot be set.
Add general.timezone_override (IANA name, validated with pendulum):
when set, general.timezone returns it and the lookup is skipped. When
unset (default) the lookup is unchanged.

Tests that patched the moved names now patch them at their source.
A new test starts the server module in a subprocess and checks that
none of these modules is loaded.

Co-authored-by: Christin <christin@BigBrother.bikini.bottom.zone>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

src/akkudoktoreos/prediction/weatherclearoutside.py

@@ -17,7 +17,6 @@ from typing import Any, Dict, List, Optional, Tuple
 
 import pandas as pd
 import requests
-from bs4 import BeautifulSoup
 from loguru import logger
 
 from akkudoktoreos.core.cache import cache_in_file
@@ -140,7 +139,9 @@ class WeatherClearOutside(WeatherProvider):
         # Get ClearOutside web content - either from site or cached
         response = self._request_forecast(force_update=force_update)  # type: ignore
 
-        # Scrape the data
+        # Scrape the data (bs4/lxml are only needed by this provider)
+        from bs4 import BeautifulSoup
+
         soup = BeautifulSoup(response.content, "html.parser")
 
         # Find generation data