Add enum handling to schema generation

[Jayanaka-98]

Enum Semantic Strings Support

Adds compile-time extraction of semantic strings from enum members, propagating them to LLM tool schemas.

Changes

• Compiler: New _extract_enum_info() in MTIR pass extracts enum members, values, and semstrings
• Schema: Updated _type_to_schema() to include enum member descriptions in generated schemas
• Tests: 6 new tests covering enum extraction and schema generation

Example

enum Personality { INTROVERT, EXTROVERT, AMBIVERT }

sem Personality.INTROVERT = "Person who is reserved and prefers solitude.";
sem Personality.EXTROVERT = "Person who is outgoing and energized by interaction.";

These descriptions now appear in the LLM schema, improving enum selection accuracy.