chore(context): refactor for consistency, optimize formatting, and simplify logic

- Cleaned up unnecessary comments in `__all__` definitions for better readability.
- Adjusted indentation and formatting across modules for improved clarity (e.g., long lines, logical grouping).
- Simplified conditional expressions and inline comments for context scoring and ranking.
- Replaced some hard-coded values with type-safe annotations (e.g., `ClassVar`).
- Removed unused imports and ensured consistent usage across test files.
- Updated `test_score_not_cached_on_context` to clarify caching behavior.
- Improved truncation strategy logic and marker handling.

backend/tests/services/context/test_ranker.py

@@ -1,7 +1,5 @@
 """Tests for context ranking module."""
 
-from datetime import UTC, datetime
-
 import pytest
 
 from app.services.context.budget import BudgetAllocator, TokenBudget
@@ -230,9 +228,7 @@ class TestContextRanker:
             ),
         ]
 
-        result = await ranker.rank(
-            contexts, "query", budget, ensure_required=False
-        )
+        result = await ranker.rank(contexts, "query", budget, ensure_required=False)
 
         # Without ensure_required, CRITICAL contexts can be excluded
         # if budget doesn't allow
@@ -246,12 +242,8 @@ class TestContextRanker:
         budget = allocator.create_budget(10000)
 
         contexts = [
-            KnowledgeContext(
-                content="Knowledge 1", source="docs", relevance_score=0.8
-            ),
-            KnowledgeContext(
-                content="Knowledge 2", source="docs", relevance_score=0.6
-            ),
+            KnowledgeContext(content="Knowledge 1", source="docs", relevance_score=0.8),
+            KnowledgeContext(content="Knowledge 2", source="docs", relevance_score=0.6),
             TaskContext(content="Task", source="task"),
         ]