Implement struct field index queries (fixes #216)

[aspizu]

Summary

This PR implements support for index queries on struct list fields, resolving issue #216.

What was implemented

• Struct field access: Added support for syntax in the method
• Index queries: Extended handling to support struct field access as RHS
• Qualified names: Proper generation of qualified names like

Example Usage

Technical Details

• expr_dot method: Now handles struct list field access by checking if the base name refers to a struct list, validating the field exists in the struct definition, and generating qualified names using
• BinOp::In extension: Modified to recognize when RHS is a field access expression and use the qualified field name for the list contains operation
• Code generation: Generates proper Scratch blocks for the qualified field names

Testing

Added comprehensive test cases covering:

• Basic struct field index queries
• Multiple struct lists with same field names
• Both existing and non-existing value queries
• Different field types (string fields in examples)

Fixes #216

[aitchFactor]

It looks like compiling a project with this feature in use fails to create a valid project. An error message I got from one such attempt is below:

FWIW, this is the same error as what occurs if the user tries to use index query on a struct list (without specifying a field) in the latest stable commit.