fix: address PR review threads - test assertions, ruff violations, format_kb consistency

Resolves review threads:
- PRRT_kwDOO6Hdxs5vNroH (Thread 36): tests now verify generic ToolError message
  instead of raw exception text (security: no sensitive data in user-facing errors)
- PRRT_kwDOO6Hdxs5vNuYg (Thread 14): format_kb KB branch now uses :.2f like all
  other branches (consistency fix)
- I001/F841/PERF401: fix ruff violations in http_layer, integration, safety tests

Changes:
- tests/test_array.py: match "Failed to execute array/parity_status" (not raw error)
- tests/test_keys.py: match "Failed to execute keys/list" (not raw error)
- tests/test_notifications.py: match "Failed to execute notifications/overview" (not raw error)
- tests/test_storage.py: update format_kb assertion to "512.00 KB" (:.2f format)
- tests/http_layer/test_request_construction.py: remove unused result var (F841)
  + fix import sort (I001)
- tests/safety/test_destructive_guards.py: use list.extend (PERF401) + fix import sort
- unraid_mcp/core/utils.py: format_kb returns f"{k:.2f} KB" for sub-MB values

Co-authored-by: @coderabbitai
Co-authored-by: @cubic-dev-ai
Co-authored-by: @copilot-pull-request-reviewer

tests/safety/test_destructive_guards.py

@@ -10,6 +10,10 @@ from unittest.mock import AsyncMock, patch
 
 import pytest
 
+# Centralized import for make_tool_fn helper
+# conftest.py sits in tests/ and is importable without __init__.py
+from conftest import make_tool_fn
+
 from unraid_mcp.core.exceptions import ToolError
 
 # Import DESTRUCTIVE_ACTIONS sets from every tool module that defines one
@@ -24,10 +28,6 @@ from unraid_mcp.tools.rclone import MUTATIONS as RCLONE_MUTATIONS
 from unraid_mcp.tools.virtualization import DESTRUCTIVE_ACTIONS as VM_DESTRUCTIVE
 from unraid_mcp.tools.virtualization import MUTATIONS as VM_MUTATIONS
 
-# Centralized import for make_tool_fn helper
-# conftest.py sits in tests/ and is importable without __init__.py
-from conftest import make_tool_fn
-
 
 # ---------------------------------------------------------------------------
 # Known destructive actions registry (ground truth for this audit)
@@ -126,9 +126,11 @@ class TestDestructiveActionRegistries:
         missing: list[str] = []
         for tool_key, mutations in all_mutations.items():
             destructive = all_destructive[tool_key]
-            for action_name in mutations:
-                if ("delete" in action_name or "remove" in action_name) and action_name not in destructive:
-                    missing.append(f"{tool_key}/{action_name}")
+            missing.extend(
+                f"{tool_key}/{action_name}"
+                for action_name in mutations
+                if ("delete" in action_name or "remove" in action_name) and action_name not in destructive
+            )
         assert not missing, (
             f"Mutations with 'delete'/'remove' not in DESTRUCTIVE_ACTIONS: {missing}"
         )