Feat: Improvement of the Custom Function Code Feature (CFC)

[dkoehler-dev]

This pull request improves the existing Custom Function Code CFC69 implementation. In particular, it includes:

• Renaming from "WriteCustomFunctionCode" to "SendCustomFunctionCode"
• An updated documentation of the CFC69 request (SCFC_README.md)
• A custom client & server example to test the CFC69 request separate from the standard function codes (examples/custom_client.rs & examples/custom_server.rs)
• Support for a variable length of CFC input arguments
• Improved unit test cases

The Client and Server now include these improvements. The code changes were tested with the extended CFC69 unit tests and the existing integration test and should work as expected. Please let me know if you have any issues or questions when reviewing the code.

These improvements were made by Dominik Köhler in the name of Iniationware GmbH and initialized by Klaus Landsdorf.

Dominik Köhler, Freelancer @Iniationware

[dkoehler-dev]

I've updated the code with some additional improvements. In particular, the PR include now:

• Support for dynamically handling all CFC requests (65-72 & 100-110), given they are implemented by the server
• An updated version of the CFC request documentation
• Updated unit tests and integration test
• An updated CFC request, including the 'byte_count_in' and 'byte_count_out' fields to dynamically parse the request
• Serial test case bugfix

Let me know if you got any question or anything to add.

These improvements were made by Dominik Köhler in the name of Iniationware GmbH and initialized by Klaus Landsdorf.

Dominik Köhler, Freelancer @Iniationware