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/core/ems.py

@@ -17,7 +17,6 @@ from akkudoktoreos.core.coreabc import (
 from akkudoktoreos.core.emplan import EnergyManagementPlan
 from akkudoktoreos.core.emsettings import EnergyManagementMode
 from akkudoktoreos.core.pydantic import PydanticBaseModel
-from akkudoktoreos.optimization.genetic0.genetic0 import Genetic0Optimization
 from akkudoktoreos.optimization.genetic0.genetic0params import (
     Genetic0OptimizationParameters,
 )
@@ -428,6 +427,12 @@ class EnergyManagement(
 
                 # --- Optimization (CPU-bound → MUST offload) ---
                 try:
+                    # Imported on first use: a server that runs GENETIC never needs
+                    # the GENETIC0 optimizer and its simulation.
+                    from akkudoktoreos.optimization.genetic0.genetic0 import (
+                        Genetic0Optimization,
+                    )
+
                     genetic0_optimization = Genetic0Optimization(
                         verbose=bool(self.config.server.verbose),
                         fixed_seed=genetic0_seed,