string, where this package is from like, "CRAN", "GitHub", only
for output message display purpose
time_out
numeric, how long to wait before reaching the time limit. Sometimes
there are too many pkgs installed and takes too long to scan the whole list.
Set this timeout in seconds to prevent the long waiting.
on_timeout
expressions, call back experssions to run when reaches timeout time.
Default is return FALSE as indicating
that package is missing (we can't find the package).
Value
vector of strings, of missing package names, character(0) if no missing