A user-defined CLI shortcut. When tess --<group_name> appears in argv,
the group’s flags are expanded inline and remaining positionals become
--filter arguments.
Load all formats: built-ins first, then any in ~/.config/tess/formats.toml
(which override built-ins of the same name). Returns the compiled map keyed
by format name.
Load all user-defined groups from ~/.config/tess/formats.toml. Built-ins
are not provided — groups are entirely user-defined. Validates that group
names don’t shadow built-in flag names.