Feature: add OpenMP in XC_Functional_Libxc::v_xc_libxc()

[linpeize]

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[mohanchen]

I would like to provide a professional suggestion regarding the usage of ModuleBase::Timer.
It is recommended that timers be placed only at the beginning and end of a function, with the timer name consistent with the function name.
It is strongly discouraged to insert timers inside a function, especially using multiple timers within a single function.
If you find it necessary to time only a specific code segment inside a function rather than the entire function, this indicates that the corresponding code block should be refactored. In most cases, the logic being timed should be extracted into a separate function, with the timer applied at the start and end of this new function.
Adding unit tests for such extracted functions is further recommended.