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>

openapi.json

@@ -6737,6 +6737,22 @@
             "title": "Longitude",
             "description": "Longitude in decimal degrees within -180 to 180 (\u00b0)",
             "default": 13.405
+          },
+          "timezone_override": {
+            "anyOf": [
+              {
+                "type": "string"
+              },
+              {
+                "type": "null"
+              }
+            ],
+            "title": "Timezone Override",
+            "description": "IANA timezone name, e.g. 'Europe/Berlin'. If set, 'timezone' is this value instead of the timezone looked up from latitude and longitude, and the lookup data (~25 MB) is never loaded. Defaults to None (look up).",
+            "examples": [
+              null,
+              "Europe/Berlin"
+            ]
           }
         },
         "type": "object",
@@ -6829,6 +6845,22 @@
             "description": "Longitude in decimal degrees within -180 to 180 (\u00b0)",
             "default": 13.405
           },
+          "timezone_override": {
+            "anyOf": [
+              {
+                "type": "string"
+              },
+              {
+                "type": "null"
+              }
+            ],
+            "title": "Timezone Override",
+            "description": "IANA timezone name, e.g. 'Europe/Berlin'. If set, 'timezone' is this value instead of the timezone looked up from latitude and longitude, and the lookup data (~25 MB) is never loaded. Defaults to None (look up).",
+            "examples": [
+              null,
+              "Europe/Berlin"
+            ]
+          },
           "timezone": {
             "anyOf": [
               {
@@ -6839,7 +6871,7 @@
               }
             ],
             "title": "Timezone",
-            "description": "Computed timezone based on latitude and longitude.",
+            "description": "Timezone: 'timezone_override' if set, else looked up from latitude and longitude.",
             "readOnly": true
           },
           "data_output_path": {