Refactor test cases for improved readability and consistency

- Updated test functions in various test files to enhance code clarity by formatting long lines and improving indentation.
- Adjusted assertions to use multi-line formatting for better readability.
- Added new test cases for theme settings API to ensure proper functionality.
- Ensured consistent use of line breaks and spacing across test files for uniformity.

tests/e2e/test_costs.py

@@ -55,7 +55,9 @@ def test_create_capex_and_opex_items(page: Page):
     ).to_be_visible()
 
     # Verify the feedback messages.
-    expect(page.locator("#capex-feedback")
-           ).to_have_text("Entry saved successfully.")
-    expect(page.locator("#opex-feedback")
-           ).to_have_text("Entry saved successfully.")
+    expect(page.locator("#capex-feedback")).to_have_text(
+        "Entry saved successfully."
+    )
+    expect(page.locator("#opex-feedback")).to_have_text(
+        "Entry saved successfully."
+    )