test(spp_cel_vocabulary,spp_gis_indicators): add tests for 95%+ coverage

spp_cel_vocabulary (34 new tests):
- _ensure_concept_groups() idempotency and completeness
- _ensure_registered() lazy registration mechanism
- head() function: missing code, _membership/_group params, fallbacks
- VocabularyCache.clear() reset behavior
- Translator error paths: unknown helpers, empty groups, unsupported ops
- code() function edge cases with falsy values
- post_init_hook() integration

spp_gis_indicators (27 new tests):
- Quantile breaks: empty values, few unique values
- Legend HTML: empty breaks, missing color scale
- get_feature_colors(): no indicators, None values, value=0, boundaries
- _get_indicator_values(): incident filter, empty period
- _compute_break_values(): no data, unknown classification
- Color scale: diverging edge cases, exact boundaries
- colors_json validation: empty string, short hex

Author: emjay0921

spp_cel_vocabulary/tests/__init__.py

@@ -1,5 +1,6 @@
 # Part of OpenSPP. See LICENSE file for full copyright and licensing details.
 
 from . import test_cel_vocabulary
+from . import test_init_and_coverage
 from . import test_vocabulary_cache
 from . import test_vocabulary_in_exists