DAOS-17088 gurt: add d_gettime_coarse() for fast timers

[soumagne]

Add d_timeless() for time comparison

Align d_timediff() to pass in pointers

Add d_timenull() and d_time_ms() for conversion

Update tests

Add missing D_COND_INIT() / D_COND_DESTROY()

Required-githooks: true

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• Two review approvals and any prior change requests have been resolved.
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• Any tests skipped by the ticket being addressed have been run and passed in the PR.

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[github-actions]

Ticket title is 'Improve gurt timers to provide fast timers'
Status is 'Open'
https://daosio.atlassian.net/browse/DAOS-17088