v7.2.4

refactor: compact codebase, rename helpers, fix error() and run_flatpak

- Rename step/success/err -> st/sc/err; make error() proxy to err "$1"
- Rename display_ver -> dpver, agressive_mode -> agrmode, list_aur -> lsaur
- Rename tester -> ntest, list_aur() -> ls_aur()
- Refactor detback() and logback() to use for loop over yay/paru/pikaur
- Absorb get_upd() into check_updates(); move jay-bin check there
- Fix run_flatpak: check use_flatpak and flatpak presence before dry_run block
- Inline detect_country() into refresh_mirrors()
- Rename MSG_MIRRORS_SUCCESS/MSG_SNAP_SUCCESS -> MSG_MIRRORS_sc/MSG_SNAP_sc
- Remove dead section comments (## !VARS, ## !FUNCTIONS, etc.)
- Collapse log_rotate/detback/load_lang onto single line
- Remove blank lines between arg-parse statements