Refactor and improve MongoDB query handling and testing

[jgaleotti]

• Introduced QueryOperationWithField to eliminate redundancy and unify field name handling across query operations.
• Refactored MongoHeuristicsCalculator:
  • Extracted computeDistanceDocuments method for better encapsulation of document calculations.
  • Renamed methods for improved clarity and consistency.
  • Updated and added related tests to ensure correctness.
• Enhanced MongoDB query selectors:
  • Utilized constant operators.
  • Added null checks to improve robustness.
  • Improved readability of the code.
• Added comprehensive tests:
  • Covered invalid empty $and, $or, $nor queries.
  • Tested empty $all query scenario.
  • Introduced QueryParserTest for better test coverage.