The fastest one I found (the only one I tried that was faster than the /(.).*\1/ variations) was certainly not the shortest:

$digits =~ /^(?=.*?0)(?=.*?1)(?=.*?2)(?=.*?3)(?=.*?4)(?=.*?5)(?=.*?6)(
+?=.*?7)(?=.*?8)(?=.*?9)/;
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But it was about twice as fast.

Update: Added the '^' to make failure cases fast.

The (?=.*?0) asserts that $digits contains a '0'. If that fails, then the regex fails. If a '0' is found, then (since that was a look-ahead assertion), we start over at the beginning of $digits and (?=.*?1) asserts that $digits contains a '1'. etc.