rust: i2c: add basic I2C device and driver abstractions

rust: i2c: add basic I2C device and driver abstractions

Implement the core abstractions needed for I2C drivers, including:

* `i2c::Driver` — the trait drivers must implement, including `probe`

* `i2c::I2cClient` — a safe wrapper around `struct i2c_client`

* `i2c::Adapter` — implements `driver::RegistrationOps` to hook into the
  generic `driver::Registration` machinery

* `i2c::DeviceId` — a `RawDeviceIdIndex` implementation for I2C device IDs

Acked-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Igor Korotin <igor.korotin.linux@gmail.com>
Link: https://patch.msgid.link/20251116162144.171469-1-igor.korotin.linux@gmail.com
[ Remove unnecessary safety comment; fix rustdoc `Device` -> `I2cClient`.
  - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>