Fix computation of barotropic streamfunction

[xylar]

This merge includes several fixes:

• Most important, the computation of the BSF only includes one constraint on the mean BSF at boundary vertices above 45 deg. S. Previously, the computation attempted to make the BSF zero on all boundary vertices, which is not correct since the value on isolated boundaries (e.g. the coast of South America vs. Antarctica) should differ by the transport between them.
• The full velocity (including bolus and submesoscale components) is used instead of just the resolved.
• The mask for transport has been fixed to correctly identify the deepest level on an edge.

The colormap has been changed (to blue-orange-div) to indicate a clear break with the incorrect BSF plots before this fix and to slightly improve the contrast at high absolute values of the BSF.

The code has been linted to follow PEP8 conventions

Checklist

• User's Guide has been updated
• If this PR adds a new analysis task, it has also been added to the user's guide
• Documentation has been built locally and changes look as expected
• Testing comment in the PR documents testing used to verify the changes

Fixes #1061

[xylar]

Testing

I have run this on the v3.LR.piControl simulation:
https://web.lcrc.anl.gov/public/e3sm/diagnostic_output/ac.xylar/analysis/v3.LR.piControl/ts_0001-0100_climo_0051-0100/ocean/index.html

Here is the corresponding previous MPAS-Analysis run:
https://web.lcrc.anl.gov/public/e3sm/diagnostic_output/ac.golaz/E3SMv3/v3.LR.piControl/mpas_analysis/ts_0001-0100_climo_0051-0100/ocean/index.html

Here is the SSH:

Here is the old BSF:

[xylar]

@irenavankova, please feel free to have a look as well, since this fix affects your work, too.

[xylar]

Test Suite

I ran the test suite and results are here:
https://web.lcrc.anl.gov/public/e3sm/diagnostic_output/ac.xasay-davis/analysis_testing/chrysalis/fix-bsf/

[milenaveneziani]

Looks great to me @xylar!
Approved based on test results and code inspection.

[xylar]

Thank you for having a look, @milenaveneziani!

[maltrud]

thanks @xylar for diving into this so quickly. looks good to me.

[maltrud]

Approved based on test results and code inspection.

[xylar]

Thanks @maltrud. The sooner this gets fixed, the less embarrassing it will continue to be for me.