Add a new message-level option (inline_encode) that causes the code
generator to inline sub-message encoding directly into the parent's
encode/calculate_size methods instead of going through the
encode_sub_message function pointer indirection.
When set on a sub-message type, the generator:
- Inlines field encoding directly (no function pointer, no backpatch overhead)
- Inlines size calculation (no separate method call)
- Skips generating standalone encode/calculate_size methods
- Validates at generation time that max encoded size < 128 bytes
Applied to BluetoothLERawAdvertisement which is encoded 12 times per
BLE advertisement batch in a hot loop.