SF bugfixes in path_finder

[Luke-Poeppel]

Fixes #197.

• There's still an onset range bug with split_extractions. See the series of Proceleusmatic in SF1.
• I added a condition to ensure any remaining sinks that aren't in the path (but still can be) are chosen. But SF1 ignores a viable trochee at the end.
• It seems like Tribrachs are getting consistently ignored... Probably good idea to add Ditribrach for consitency. Might solve some of this.

[codecov-commenter]

Codecov Report

Merging #198 (4a120e4) into dev (1d8ee49) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              dev     #198   +/-   ##
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  Coverage   78.46%   78.46%           
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  Files          17       17           
  Lines        2401     2401           
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  Hits         1884     1884           
  Misses        517      517