[ftr] Add `4 bit` interface support

### Description
As the `HD44780` datasheet states, it's possible to have 2 types of interfaces to interact with the display:
- `4 bit`
- `8 bit`

The `8 bit` one is already implemented, but `4 bit` one is missing.

### Acceptance criteria
It's possible to manipulate the display using `4 bit` interface and the display behaves as the datasheet specifies.

Start by locating the existing 8-bit interface implementation and reading the HD44780 datasheet sections covering 4-bit operation. Use the current interface behavior as the reference, then verify that display manipulation follows the datasheet and that the 4-bit interface behaves correctly alongside the existing 8-bit support.

Written by the indexing model from the issue text.