Migrate fields parser and transformers module from Javascript to Rust

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What does this MR do and why?

This merge request implements the migration of fields parser and transformers in the GLQL Rust implementation. The changes include:

1. Fields Parser Migration:
   • Implemented a robust parser for field names and field lists using nom parser combinator
   • Added support for field transformers through function syntax (e.g. labels("workflow::*"))
   • Enhanced error handling for invalid field formats and missing fields
   • Added comprehensive test coverage for field parsing scenarios
2. Field Transformers:
   • Implemented field transformation logic for various field types (string, number, date, boolean)
   • Added support for field aliasing and field type validation
   • Implemented field function transformers (e.g. label pattern matching)
   • Added context-aware field transformation based on source type (Issues/MRs)

Related to #27 (closed)

The changes can be validated by:

• Running the test suite which includes new test cases for field parsing and transformation
• Testing complex queries with field transformers
• Verifying error messages for invalid field usage
• Checking integration with both Issues and Merge Requests queries