Improve coverage from 37.97% to 40.64% with tests for:
- PDU types in SNMPv3 messages (get_next, get_response, set, getbulk)
- Context engine ID and context name (empty, non-empty, both)
- Message max size variations (minimum 484, custom values)
- Multiple varbinds in v3 messages
- Error responses with various error_status values (0-5)
- Reportable flag variations (true/false)
- USM security model
- All SNMP value types (counter64, gauge32, ip_address, opaque, oid)
- Exception values (no_such_object, no_such_instance, end_of_mib_view)
- Message ID edge cases (0, max 2147483647)
- Discovery message consistency
Tests verify message encoding completes without crashes
even when V3 security processing is involved.
Coverage: 1,391 → 1,419 tests, all passing
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
