Spelling test: don't fail on words found only in NEWS.md

[ms609]

NEWS.md routinely names new technical terms, which made the spelling test fail until they were added to inst/WORDLIST (as happened with POPCNT/CPUID on ms609/TreeTools#288).

tests/spelling.R now calls spelling::spell_check_package() directly. It uses the same source-directory lookup and the same skip on CRAN (NOT_CRAN) as spell_check_test(). Words found only in NEWS.md are printed and do not fail the test; words found anywhere else still stop it. Add the NEWS-only words to the WORDLIST at release.

Same change as agent-issues/TreeSearch#192. Checked with local R 4.6.1: the script runs, and classifies words by where they occur.

[github-actions]

Performance benchmark results

Call	Status	Change	Time (ms)
ClusteringInfoDistance(tr280)	⚪ NSD	0.98%	9.84, 9.6 → 9.68, 9.6
ClusteringInfoDistance(tr50)	⚪ NSD	-0.14%	6.67, 6.53 → 6.71, 6.45
LAPJV(test2000)	⚪ NSD	-3.55%	105, 106 → 107, 112
LAPJV(test40)	⚪ NSD	-0.33%	0.0184, 0.0184 → 0.0186, 0.0183
LAPJV(test400)	⚪ NSD	-0.18%	3.31, 3.3 → 3.32, 3.3
MutualClusteringInfo(tr280)	⚪ NSD	-0.53%	20.3, 19.4 → 19, 20.4
MutualClusteringInfo(tr50)	⚪ NSD	-2.21%	18.9, 17.3 → 17.6, 18.1
NNIMaxStep(2000, normalize = TRUE)	⚪ NSD	0.06%	0.185, 0.184 → 0.185, 0.184
NNIMaxStep(300, normalize = TRUE)	⚪ NSD	0.27%	0.03, 0.0302 → 0.03, 0.03
NNIMaxStep(300)	⚪ NSD	0.23%	0.00827, 0.00832 → 0.00829, 0.00827
PathDist(postTrees)	⚪ NSD	-0.25%	2.56, 2.56 → 2.57, 2.56
PhylogeneticInfoDistance(tr180)	⚪ NSD	-3.45%	60.5, 60.3 → 62.7, 60.1
PhylogeneticInfoDistance(tr50)	⚪ NSD	-2.31%	42.2, 42.3 → 43.4, 42.3
RobinsonFoulds(tr280)	⚪ NSD	0.31%	4.68, 4.64 → 4.63, 4.65
RobinsonFoulds(tr280)	⚪ NSD	0.7%	4.48, 4.54 → 4.46, 4.47
RobinsonFoulds(tr50)	⚪ NSD	-0.8%	4.36, 4.37 → 4.44, 4.38

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.57%. Comparing base (00d2b8f) to head (b0f4def).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #216   +/-   ##
=======================================
  Coverage   97.57%   97.57%           
=======================================
  Files          60       60           
  Lines        6065     6065           
=======================================
  Hits         5918     5918           
  Misses        147      147           

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