Fix #413, Add coverage tests for pc-rtems

[thnkslprpt]

Checklist

• [x] I reviewed the Contributing Guide.
• [x] I signed and emailed the appropriate Contributor License Agreement to GSFC-SoftwareRelease@mail.nasa.gov and copied cfs-program@lists.nasa.gov.

Describe the contribution

• Fixes #413
  • Adds coverage tests for pc-rtems implementation (some function are just placeholders anyway, but the coverage tests are there for users to amend for their implementation).
  • Minor clean-up of CMakeLists.txt files etc.

Testing performed GitHub CI actions all passing successfully and local testing results in the following added coverage for pc-rtems:

Expected behavior changes No code changes - only adding new tests.

System(s) tested on Debian GNU/Linux 11 (bullseye) Current main branch of cFS bundle.

Contributor Info Avi Weiss   @thnkslprpt

[thnkslprpt]

I wasn't able to easily set up the context enough to test CFE_PSP_WriteToCDS and CFE_PSP_ReadFromCDS fully - if someone can get it working I'll add it in.

[skliper]

Recommending CCB review (and hopefully merge) so we can continue moving forward.

Future work: Minor coverage improvements, add to CI and enforce (already #18), stub out shared APIs and cover those in their own test cases, individual exe per file.