Added optional flag to time_interp_external to speedup initialization

[MJHarrison-GFDL]

Description

time_interp_external_nml:check_uniform_times=.true. will enable this option which performs a time axis check for uniformly spaced time levels prior to attempting to read the entire axis. In some cases, this will significantly reduce initialization time when reading large input files via data_override for example. It is possible that enabling this option
will result in answer changes in some configurations, so it is currently being set False by defauly.

Fixes # (issue)

How Has This Been Tested?

Using a stand-alone driver. Tested for single threading only.

Checklist:

• My code follows the style guidelines of this project
• [x ] I have performed a self-review of my own code
• [ x] I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• [ x] My changes generate no new warnings
• [ x] Any dependent changes have been merged and published in downstream modules
• [ x] New check tests, if applicable, are included
• make distcheck passes

[thomas-robinson]

@MJHarrison-GFDL Thank you for the PR. Can you include a test that tests the functionality so we can include it in our test suite. Also, can you opne an issue describing the problem you are trying to solve.

[MJHarrison-GFDL]

@thomas-robinson . The test I used is located on gaea : /lustre/f2/dev/Matthew.Harrison/tmp/FMS_fast_data_override/test . Initialization time went from 5min -> 2sec.

[thomas-robinson]

@MJHarrison-GFDL that's great! Do you need help getting this test into the FMS test suite?