v0.8.4

• Lexer/Parser/AST:
  Full and proper support for array indexing in object references and lvalue
  assignments; parser and listener logic updated accordingly.
  Bug fix: Properly lex isolated digits in heredoc content and escaped dollar
  signs in string interpolations.
  Improved error handling: Parser errors are now propagated to listeners and
  main program logic, enabling better diagnostics and LSP support.
  Added new test cases for parser errors and self-reference outside of class
  context.
  Bug fix: Verify we're inside a class if processing a self-reference.
  Improved output line comparison in the test suite.
• Standard Library:
  All container empty methods now return status code
  (0 if empty, 1 otherwise) instead of echoing "true"/"false", for
  shell-friendly checks.
  Documentation and test cases updated to reflect new empty method behavior
  Consistent return conventions across Array, Stack, Queue, SharedArray,
  SharedStack, SharedQueue, SharedVar, TypedArray, TypedStack, and TypedQueue
• Documentation:
  Added and clarified language specification pages, including a new page on
  the "entity" concept.
  Improved CONTRIBUTING.md with style guidelines and examples.
  Added PR template and clarified how to add test cases.
• Language Server:
  Bug fix: If the input stream is halted, clean up and exit rather than
  hanging.
  Improved debounce logic for didChange notifications.
  Bug fix: Provide completions after 'this'/'super' keywords.
  Improved error propagation and diagnostics for parser errors.