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.