Fix #413, Add coverage tests for pc-rtems

[thnkslprpt]

Checklist

• I reviewed the Contributing Guide.
• 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 Coverage tests missing for pc-rtems #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]

Great work! Apologies it took so long to get to a review. A few minor nits below and recommend a rebase on main and should be good to go!

Eventually it'd be nice to restructure slightly to split into separate executables like apps do it (same change for the VxWorks ut's), and separate the shared test from the VxWorks one but I recommend getting this PR in before tackling those restructuring changes. I can also help w/ the final few uncovered lines (although lets get this in first).

[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.