enforce final newlines and trim trailing whitespace

- Having trailing newlines makes diffs more readable when files are extended with more lines. Otherwise it creates unnecessary diffs which look like 2 lines have been modified (the last line and the new content).

- It's already being enforced by most code linters such as Ruff anyway, so our EditorConfig went against our linter.

- We should also enforce trimming of any trailing whitespace fluff at the end of lines.

.editorconfig

@@ -3,7 +3,8 @@ charset = utf-8
 end_of_line = lf
 indent_size = 4
 indent_style = space
-insert_final_newline = false
+trim_trailing_whitespace = true
+insert_final_newline = true
 max_line_length = 120
 tab_width = 4
 ij_continuation_indent_size = 8