add rust symbol model

[rithulkamesh]

Borrowed from Java, Implemented the following:

Core components:

1. Basic Symbol Structure

• Track modules, functions, types and traits
• Handle Rust visibility modifiers
• Support generics and lifetimes
• Track attributes and documentation
• Support module hierarchy and crates

2. Type System

• Handle structs, enums, unions and traits
• Support type parameters and bounds
• Track implementations and trait bounds
• Handle associated types

3. Function Analysis

• Track parameters and return types
• Support async, const and extern functions
• Handle generics and where clauses
• Track call sites and dependencies

4. Safety Analysis

• Classify functions as safe/unsafe/FFI
• Track unsafe blocks and their reasons
• Add safety statistics for crates
• Split module functions into safe/unsafe collections
• Track raw pointer usage and FFI interactions