Ensure no warning or errors when no extrapolation occurs

[Sparks29032]

In #255, self.extrapolation_info was not set as a class variable. As such, there are cases where the code seeks to reference this value when it is not defined, producing an error.

For example, when a morph function without extrapolation warnings (e.g. scale) is used with one with warnings (e.g. stretch) and the the one with warnings does not extrapolate (e.g. --scale=1 --stretch=0), this will produce an error.
Tests are now added to cover this case in the future.

Please merge this asap. We may need to do a 0.3.1 release and scrap the 0.3.0 one on conda-forge since this error is not rare.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.93%. Comparing base (177d073) to head (d3e5a91).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #278   +/-   ##
=======================================
  Coverage   99.93%   99.93%           
=======================================
  Files          24       24           
  Lines        1446     1480   +34     
=======================================
+ Hits         1445     1479   +34     
  Misses          1        1           

Files with missing lines	Coverage Δ
tests/test_morphshift.py	100.00% <100.00%> (ø)
tests/test_morphsqueeze.py	100.00% <100.00%> (ø)
tests/test_morphstretch.py	100.00% <100.00%> (ø)

🚀 New features to boost your workflow:

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