fix(parser): correctly handle empty documents in multi-document yaml

[semihbkgr]

It fixes a bug where parsing a multi-document yaml file with an empty document (--- with no content) would cause the parser to stop processing subsequent documents. The document token grouping logic in parser is updated to ensure every document boundary (---), even if empty, results in a document token. Parsing continues after empty documents.

fixes #765

As I am not fully familiar with the codebase, I am not certain this is the best or most complete fix and welcome feedback or suggestions for additional test coverage.

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.95%. Comparing base (81dbf26) to head (1a8acaa).
Report is 41 commits behind head on master.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #767      +/-   ##
==========================================
+ Coverage   77.34%   77.95%   +0.60%     
==========================================
  Files          22       22              
  Lines        7905     8100     +195     
==========================================
+ Hits         6114     6314     +200     
+ Misses       1372     1370       -2     
+ Partials      419      416       -3     

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