Include mode in pitchFromDegree cache key (fixes #1535)

[bingliscodes]

Fixes #1535

Add self.mode attribute to the AbstractScale base class and store the raw mode on AbstractOctatonicScale and AbstractDiatonicScale at the end of buildNetwork to keep mode and pitch network consistent.

Add mode derived from the abstract scale to the _PitchDegreeCacheKey to ensure scales that share the same type and tonic but different modes no longer share cache entries. Since the key is a tuple and some modes are lists (and can't be dict keys), they are converted with str(mode).

Three regression tests in test_scale_main.py covering two octatonic modes, two diatonic modes, and swapping .abstract

Notes for maintainers

• The cache key now reads the abstract scale's mode, so changing .abstract.mode manually without calling buildNetwork isn't supported, related to Changing a key's mode attribute is ignored by key.romanNumeral() #1478.

[coveralls]

coverage: 93.364% (+0.005%) from 93.359% — bingliscodes:fix-1535-octatonic-mode-cache into cuthbertLab:master

[mscuthbert]

Thanks! Great!