BUGFIX Earley: Now yielding a previously repressed ambiguity

[erezsh]

Contains 3 commits:

1. Test test_multiple_start_solutions, that fails before the fix

2. Fixes Earley. Previously, slightly different items were considered equal.

3. A fix to the test_cycle2, which I believe was previously wrong

Issue #1424 was the first lead to finding this bug. But seems that it isn't solved by this change alone.

@chanicpanic Can you please verify my work?

[erezsh]

P.S. It's easier to see why there should be ambiguity in test_cycle2, if we rename _recurse to recurse. The second recurse is now taken, and was previously ignored. (i.e. it's a new path, not an extra cycle)

[chanicpanic]

LGTM with a couple optional comments.

While this doesn't fully solve the issue from #1424, it does appear to fix all the examples in #536.

[erezsh]

@chanicpanic Like that?

[chanicpanic]

Yup, looks good

[erezsh]

@MegaIng Any comments? Or should I just merge it?

[MegaIng]

I can't say much on the actual implementation changes since I don't know the earley algorithm well enough, but looks good in general.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 90.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 89.54%. Comparing base (1be22db) to head (efeb846).
Report is 8 commits behind head on master.

Files	Patch %	Lines
lark/parsers/earley.py	80.00%	2 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1427      +/-   ##
==========================================
+ Coverage   89.53%   89.54%   +0.01%     
==========================================
  Files          52       52              
  Lines        7814     7825      +11     
==========================================
+ Hits         6996     7007      +11     
  Misses        818      818              

Flag	Coverage Δ
unittests	89.54% <90.00%> (+0.01%)	⬆️

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[erezsh]

Thanks @chanicpanic and @MegaIng !