feat(golang): implement exception classname metadata extraction

[pleberre]

Problem

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

File Location

src/main/java/io/err0/client/languages/GolangSourceCodeParse.java:324

// TODO: extract exception classname meta data

Context

Go uses explicit error handling with the error interface:

// Standard error returns
func doSomething() error {
    return errors.New("something went wrong")
}

// Custom error types
type MyError struct {
    message string
}

// Error interface implementation
func (e *MyError) Error() string {
    return e.message
}

// Standard library errors
return fmt.Errorf("failed: %w", err)

Expected Behavior

Extract and store:

• Error type names from return signatures
• Custom error struct names
• Standard library error types
• Wrapped error information

Implementation Guidance

1. Identify Go error patterns:

   • error return types
   • errors.New() calls
   • fmt.Errorf() calls
   • Custom error struct definitions
   • Error type assertions

2. Extract error information:

   • For custom types: extract struct name
   • For standard errors: mark as "error"
   • For wrapped errors: extract wrapped type if available

3. Store in token metadata

4. Handle Go's convention of returning (result, error) tuples

Test Cases Needed

Add to src/test/testdata/ for Go:

• Function returning error
• Custom error type
• errors.New() usage
• fmt.Errorf() usage
• Error wrapping with %w

Reference Files

• src/main/java/io/err0/client/languages/JavaSourceCodeParse.java (exception pattern reference)
• Existing Go test data in src/test/testdata/

Acceptance Criteria

• Error type names extracted from Go error patterns
• Metadata field populated with error information
• TODO removed from GolangSourceCodeParse.java:324
• Tests pass for Go error handling
• No regressions in existing Go parsing