v1.2.5: Minor bug fixes, refactors and tests

- Fix bug where `probs.start.ok` is incorrectly `FALSE` if the
  user does not provide starting probabilities
- Fix `poLCA.posterior()` which now uses the C++ implementation.
  Previously, it did not link correctly to the C implementation
- Implement C++ versions of likelihood and posterior evaluation,
  deprecate some internal R and C functions following
- Change the nesting order of `for` loops in the E step
- Add more tests for various R functions
- Add a `R CMD check` in the dev Apptainer
- Favour `remotes` over `devtools` in documentation
- Generate all documentation using `roxygen2`
- Generate `NAMESPACE` with `usethis` and `roxygen2`