Added complete test coverage for MIB.Error module (16.13% -> target 100%):
**Error Creation:**
- All supported error types (syntax, semantic, import, type, constraint, etc.)
- Error creation with line and column information
- Error creation with context maps
- Suggestion generation for common mistakes
**Error Types Tested:**
- unexpected_token with various combinations (expected/actual/value)
- unexpected_eof with expected values
- unterminated_string
- invalid_number and invalid_identifier
- file_not_found with path
- import_error with symbol and module
- duplicate_definition with name
- Generic error types
**Suggestion Generation:**
- MAX-ACCESS vs ACCESS typo
- deprecated 'mandatory' vs 'current'
- OBJECT-TYPE vs OBJECT-IDENTITY confusion
- Unterminated string hints
- File not found with RFC/MIB name detection
- Import error dependency hints
**Error Formatting:**
- Format with/without line and column
- Format with/without suggestions
- Multiple suggestion formatting
- Edge cases (nil values, empty strings, non-standard types)
**Edge Cases:**
- All nil fields
- Large line numbers
- Zero/negative line/column values
- Various context data types
- Mixed token value types
- Empty options handling
53 new tests added
Test count: 1,211 -> 1,264 (all passing)
