Make test result parsing stricter about duration formats

Summary: Fixes T8805. Explicitly require int/float for duration. Adjust XUnit/Go parsers to provide one.

Test Plan: Ran unit tests.

Reviewers: btrahan, joshuaspence, chad

Reviewed By: chad

Subscribers: jsotuyod, champo, epriestley

Maniphest Tasks: T8805

Differential Revision: https://secure.phabricator.com/D13637