(Fix-It Week) Update VMEC object to throw an error if a boundary with a different nfp is assigned

[mishapadidar]

Summary This pull-request throws an error if a boundary is assigned to a VMEC object that has an NFP that is different from the NFP of the VMEC object.

Only two lines of code need to be added.

Tests A unit test is added to test this feature.

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 93.01%. Comparing base (489486d) to head (4bff675). :warning: Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #502      +/-   ##
==========================================
+ Coverage   92.65%   93.01%   +0.35%     
==========================================
  Files          83       83              
  Lines       16194    16197       +3     
==========================================
+ Hits        15004    15065      +61     
+ Misses       1190     1132      -58     

Flag	Coverage Δ
unittests	93.01% <100.00%> (+0.35%)	:arrow_up:

Flags with carried forward coverage won't be shown. Click here to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

:rocket: New features to boost your workflow:

• :snowflake: Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[mishapadidar]

@daringli can you take a look at this again?

[daringli]

@daringli can you take a look at this again?

I just merged in master. It's ready for review if it passes the CI.