Fix #90, Convert `int32` return codes and variables to `CFE_Status_t`

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 #90
- most int32 return codes converted over to CFE_Status_t
- int32 status/return variables holding cFE return codes converted to CFE_Status_t
- removed the Status variable from LC_AppPipe() - it was not actually used - the function always returns CFE_SUCCESS as currently implemented

Testing performed GitHub CI actions all passing successfully.

Expected behavior changes No change to behavior. CFE_Status_t is more expressive and improves consistency with cFE/cFS.

Contributor Info Avi Weiss @thnkslprpt

nasa / LC