Implement lambda shorthand syntax (x -> body)

[ochsec]

Summary

Adds support for lambda shorthand syntax x -> body as syntactic sugar for Function[{x}, body].

Changes

• Lexer: Added Arrow token to recognize -> operator, with logic to distinguish from minus operator
• Parser: Implemented desugaring of arrow syntax into Lambda expressions with single parameter
• Tests: Comprehensive test suite covering:
  • Lexer token recognition
  • Parser AST generation
  • Equivalence with explicit Function syntax
  • Code generation to Rust closures
  • Integration with Map, Filter, and pipe operations

Example

Map[x -> x * 2, [1, 2, 3]]

Desugars to:

Map[Function[{x}, x * 2], [1, 2, 3]]