Add max clock skew

[jameseaster]

Resolves #183

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What kind of change does this PR introduce?

• Feature update

What is the current behavior?

• Clock skew is not taken into consideration

What is the new behavior?

• Clock skew is considered in the time comparisons

Does this PR introduce a breaking change?

• No

How has this been tested?

• Currently, not tested as a package. I have tested the helper function compareTime locally with different values from example credentials. However, I have not been able to create the original bug that requires the maxClockSkew. More testing from other reviewers is needed.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.86%. Comparing base (545a4eb) to head (04639b6).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #189      +/-   ##
==========================================
+ Coverage   90.44%   90.86%   +0.42%     
==========================================
  Files           5        5              
  Lines        1057     1106      +49     
==========================================
+ Hits          956     1005      +49     
  Misses        101      101              

Files with missing lines	Coverage Δ
lib/helpers.js	94.21% <100.00%> (+1.01%)	⬆️
lib/index.js	91.01% <100.00%> (+0.32%)	⬆️

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