limit cos of zenith angle between -1 and 1 in ZenithAngleCalc.jl

[szy21]

Purpose

To-do

Content

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• I have read and checked the items on the review checklist.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.93%. Comparing base (6727a53) to head (20dffac).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #76   +/-   ##
=======================================
  Coverage   98.93%   98.93%           
=======================================
  Files           4        4           
  Lines          94       94           
=======================================
  Hits           93       93           
  Misses          1        1           

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