* chore: add small profile (timing) script
Run it with `make profile`, which runs scripts doing `hop.setup` with
different settings, and print the elapsed time (in nanoseconds).
This would be helpful to determine the cost of setup.
Currently mainly target on the `match_mappings` option, when all
mappings were loaded, it increases time about 0.3 ms on my machine.
* chore: load match_mappings on demand
- In setup, only prepare an empty loaded_mappings table.
- When really using the feature (only in mappings.checkout), try load
the wanted tables (e.g., zh_sc) on demand.
- Notify user if the loading failed. Rather than raising E5108 with lua
not-found error (original behavior).
