Support ReadingUnits mechanism

# 🚀 Feature Request

### Relevant Package [**REQUIRED**]

This feature request is for C Device SDK

### Description [**REQUIRED**]
In Go Device SDK, there is a ReadingUnits mechanism and configuration to allow the Event/Reading sent out from Device Services with an "Units" field
https://docs.edgexfoundry.org/4.0/microservices/device/Configuration/

### Describe the solution you'd like
Refer to the Go SDK support it
https://github.com/edgexfoundry/device-sdk-go/blob/83dc2e8a2deab4fc3d101c7c00af555ccc552454/example/cmd/device-simple/res/configuration.yaml#L4
https://github.com/edgexfoundry/device-sdk-go/blob/83dc2e8a2deab4fc3d101c7c00af555ccc552454/internal/transformer/transform.go#L114-L116

Start by reading the Go SDK references in example/cmd/device-simple/res/configuration.yaml and internal/transformer/transform.go, then locate the corresponding configuration and event-generation paths in device-sdk-c. Done means the C Device SDK supports configurable reading units and includes the Units field in emitted Events/Readings.

Written by the indexing model from the issue text.