Repair the build

[pavel-kirienko]

This is a response to https://forum.opencyphal.org/t/building-libcyphal/2427

• Added brief build instructions to the README. The point of this change is mostly to indicate that one does not need to "build" libcyphal to use it because it is header-only. Building is only needed for development or verification.
• Fixed broken coverage measurement and updated CI workflow dependencies. Oh boy.
• Fixed the missing cavl error by pulling cavl from its own repository. Libcanard does no longer ship cavl and libudpard will eventually be updated to not do that either.
• The libcanard reference was updated to master instead of v4, temporarily until v4 is out. The code that leverages libcanard has been doctored to accommodate API changes in v4 (still officially unstable but I am not planning on changing it so it's kinda stable after all).
• Treat NO_STATIC_ANALYSIS properly.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud