gh-36024: `sage -fixdoctests`: Handle directory names, call `sage -t` only once
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We change the handling of file name arguments in `sage -fixdoctests`:
Instead of calling `sage -t` on files one by one, we just pass them to
`sage -t` as a whole and then handle its output for all files. This is
much faster because of the startup overhead of `sage -t`, and also adds
the handling of directory names.
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Cherry-picked from
- #35095
Part of
- #29705
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URL: https://github.com/sagemath/sage/pull/36024
Reported by: Matthias Köppe
Reviewer(s): Kwankyu Lee, Matthias Köppe
