sud: fail fast on malformed sud.json documents, one test per fixture

Sud.load() now calls utils/sud_validate.py's validate_sud() before
parsing: requires a non-empty 'steps' list, and for every resolved
step that sets its own 'temperature', a numeric ramp.rate - the one
genuinely unguarded crash site (ramp['rate'], no .get() fallback) hit
in tasks/sud.py, components/sud_forecast.py and demo_sud.py the moment
that step is reached, which for SudForecastEstimator can be as early
as the Load itself. A refused load is now logged with the specific
reason (previously silent). validate_sud() reuses Sud._parse_data()
directly rather than reimplementing default-merging/step-building.

tests/utils/test_sud_validate_fixtures.py covers 8 fixture docs plus
all 6 real sude/*.json files; tests/components/sud/test_sud_load.py
exercises the Sud.load() wiring itself (rejects, keeps prior schedule).

Also reworked both this and test_config_fixtures.py to generate one
dedicated test method per fixture file (dynamic setattr) instead of
looping with subTest inside a single method - subTest iterations don't
show up individually in `unittest -v`/IDE test runners, which made it
look like far fewer fixtures were covered than actually are.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01F4oEE99rkKVU8L8tkzXWdG

utils/sud_validate.py

@@ -0,0 +1,33 @@
+from utils.config_validate import ConfigError, require
+from components.sud import Sud
+
+
+def validate_sud(data):
+    """Fail-fast structural check for a sud.json document - same rationale
+    as config_validate.py's validate_temp_ctrl(): a malformed field here
+    doesn't surface until deep inside a run, or worse, during
+    SudForecastEstimator's very first Load-time simulation (tasks/sud.py,
+    components/sud_forecast.py and scripts/demos/sud/demo_sud.py all read
+    ramp['rate'] directly, no .get() fallback, the moment any step actually
+    sets its own 'temperature') - as a bare KeyError with no indication of
+    which schedule step or field is wrong.
+
+    Reuses Sud._parse_data() itself (rather than re-implementing default-
+    merging/step-building) so what's checked here can never drift from what
+    actually gets parsed at runtime."""
+    require(data, 'steps', type=list)
+    if not data['steps']:
+        raise ConfigError("'steps' must be a non-empty list")
+
+    try:
+        schedule = Sud._parse_data(data)[2]
+    except (KeyError, TypeError, AttributeError) as e:
+        raise ConfigError("malformed sud document: {}".format(e))
+
+    for step in schedule:
+        if step['temperature'] is None:
+            continue
+        try:
+            require(step, 'ramp.rate', type=(int, float))
+        except ConfigError as e:
+            raise ConfigError("step {} ({}): {}".format(step['number'], step.get('descr'), e))