FreeRTOS/FreeRTOS-Cellular-Interface — reverse-engineered prompt

Build me a small production ready C library for FreeRTOS that makes cellular modems easier to use. I want it to hide the messy AT command handling and expose one simple, consistent API for common modem tasks, especially the standard 3GPP TS 27.007 commands, plus a socket style interface for TCP capable modems.

Please structure it so there is shared code for the standard commands, then a clean way to plug in modem specific behavior for vendors that need custom commands or custom unsolicited responses. It also needs an abstract communication layer so the same library can talk to a modem over UART or SPI depending on the MCU platform. Use FreeRTOS primitives for task sync and memory where needed.

Make it feel reusable and easy to port to a new modem, include clear docs and a basic integration example, and add unit tests for the core pieces. Keep the code quality high and embedded friendly. If anything is unclear, check the current FreeRTOS cellular docs online and follow the standard approach they use.