Implement Event Synchronization protocol in firmware for early delivery of changed states

[ethanjli]

This PR is a mostly one-to-one direct port of the backend's implementation of the Event Synchronization protocol from #403, but with some key differences:

• Because C++17 doesn't natively provide a == operator for structs, I had to add the Boost PFR library (documentation here) so that we can compare two instances of structs like AlarmLimits. It relies on template metaprogramming magic, but it only compares the literal contents of two instances of a struct and it doesn't seem to work for us in trying to compare the contents of arrays. So we have to define custom == operators for NextLogEvents and ActiveLogEvents. The PFR library is third-party code licensed under the Boost Software License, which is fine for our project; I'll provide some more information in the "questions for records-keeping" checklist. Due to the way nanopb works, until we address #405 we have a templated == operator in the global namespace, which means you might be able to erroneously use == and != on types which shouldn't have such an operator, or else you might see cryptic compiler errors.
• While in Python we can return None from a sender, in C++ we have to return a StateOutputStatus::none error code.

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[ethanjli]

For records-keeping:

1. This project is licensed under Apache License v2.0 for any software, and Solderpad Hardware License v2.1 for any hardware - do you agree that your contributions to this project will be under these licenses, too? Yes
2. Were any of these contributions also part of work you did for an employer or a client? No
3. Does this work include, or is it based on, any third-party work which you did not create? Yes: this PR adds the Boost PFR library as a header-only library included in the Core/Inc directory, along with its license file. The PFR library is licensed under the Boost Software License, which is a permissive license and is compatible with our project's licenses. I've recorded the use of this library, along with the license, on our Notion page for tracking third-party works and licenses.

[ethanjli]

@rohanpurohit What level of review and/or testing do you think we should apply to this PR? Do you think we should include this in milestone v0.12, or move it to v0.13?

[rohanpurohit]

@rohanpurohit What level of review and/or testing do you think we should apply to this PR? Do you think we should include this in milestone v0.12, or move it to v0.13?

It looks like I can only do light testing on this one! I assume if we go ahead with #403 we'll need to merge this too? I feel like maybe we can go ahead with it if it looks good to you on your end? sorry about not responding sooner.

[ethanjli]

Great, thanks! I had forgotten to test the alarm muting to get a sense of the latency improvements for that.