MINIFICPP-1500 Fix multiple archive tests running in parallel

[lordgamez]

The NonRepeatingStringGenerator only generated an initial prefix from the current timestamp's millisecond count. Because of this if multiple ArchiveTests (FocusArchiveTests and ManipulateArchiveTests) were run in parallel it could occur, that they generated the same temp filename due to the same timestamp. This caused failures as the different test suites manipulated each other's test files.

https://issues.apache.org/jira/browse/MINIFICPP-1500

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