function Arguments.is_explicit
Return
True iff the user passed --<name>=... (or its short form) on the CLI for the current invocation.
Returns False for args that were resolved from the task’s
default, an alias’s overridden default, or a config.axl
override — anything that wasn’t typed at the command line.
Used by repro / fix command builders to skip echoing flags
whose values would just reproduce the task’s default. The
developer copying the rendered repro gets back exactly what
they (or CI) typed.
