Wax_utils.DebugSourceDeveloper-facing debug output, enabled per category with --debug.
Known category names, for help text and error messages. Currently ["timing"].
Parse one category name; Error msg names the valid categories.
Record which debug categories are active. Call once at startup.
timed label f runs f (). When Timing is enabled, it measures the wall-clock duration of f and prints "<label>: <n> ms" to stderr; otherwise it just runs f with no measurement and no output.
timed_if cond label f is timed label f when cond holds, and f () untimed otherwise. Used to skip timing a measurement-only sub-pass (e.g. the dry trivia-collection traversal of the printer).