feat(rust): implement exception classname metadata extraction

[pleberre]

Problem

The Rust parser does not extract exception classname metadata, resulting in incomplete error tracking data.

File Location

src/main/java/io/err0/client/languages/RustSourceCodeParse.java:304

// TODO: extract exception classname meta data

Context

Rust uses Result<T, E> and panic! for error handling:

// Result type errors
let result: Result<i32, MyError> = Err(MyError::new());

// Panic macro
panic!("error message");

// Custom error types
enum MyError {
    NetworkError,
    ParseError(String),
}

Expected Behavior

Extract and store:

• Error type names from Result<T, E> patterns
• Enum variant names for error types
• Custom error struct names
• Standard library error types (io::Error, etc.)

Implementation Guidance

1. Identify Rust error patterns:

   • Result<T, E> types
   • panic! macro calls
   • Error enum definitions
   • std::error::Error trait implementations

2. Extract error type name:

   • For Result<T, MyError>: extract "MyError"
   • For panic!: mark as "panic"
   • For custom enums: extract enum name and variant

3. Store in token metadata (similar to other languages)

4. Follow existing patterns from Java exception handling

Test Cases Needed

Add to src/test/testdata/ for Rust:

• Result type with custom error
• Panic macro
• Error enum with variants
• std library errors

Reference Files

• src/main/java/io/err0/client/languages/JavaSourceCodeParse.java (exception handling pattern)
• src/main/java/io/err0/client/languages/GolangSourceCodeParse.java (similar Go error handling)

Acceptance Criteria

• Exception class names extracted from Rust error patterns
• Metadata field populated with error type information
• TODO removed from RustSourceCodeParse.java:304
• Tests pass for Rust error handling
• No regressions in existing Rust parsing