Implement independent i2c sensor readings

The types field on `ws_i2c_Add` is a proto `map`. Because nanopb has no map type, it generates a `ws_i2c_Add_TypesEntry` submessage.

The key is an index, assigned by the broker and the `value` is the sensor's SI type.

Currently, the key is plumbed E2E from an `Add` (via `EnableSensorReads()`) to an event (via `GetSensorEvent`). However, dispatching via `GetSensorEvent` is by type.

If a sensor contains 3 light sensor components, the `GetSensorEvent` will return the same `getEventLight()` handler function.

To fix this - we want to pass the full `...TypesEntry` into `GetSensorEvent()` to allow a driver to optionally switch, based on the index and optional key, to select the correct `getEventLight()`. The base driver header will also need to be modified to optionally select based on the key

Start by tracing ws_i2c_Add through EnableSensorReads() and GetSensorEvent(), then inspect the base driver header and the getEventLight() handlers. Done means GetSensorEvent() and the base driver can receive the full TypesEntry and optionally select a handler using its index or key, while preserving existing type-based behavior.

Written by the indexing model from the issue text.