Remove assert statements to support Python -O / -OO

[arunkumargururaj07-star]

This fixes test failures under Python’s optimization flags (-O / -OO).

I found that test_copy_unequal was silently passing under -O because the helper assert_layers_equal used assert statements — which get stripped when assertions are disabled.

This PR replaces all assert calls in tests/utils/assertions.py with explicit ValueError raises, so the tests behave consistently regardless of optimization level.

Also cleaned up a few commented-out assert lines for clarity.

[LarsKue]

@arunkumargururaj07-star Thank you for the PR! Unfortunately, I think the changes you made are not fully in the spirit of the corresponding issue. Since we use pytest to run the tests, the best practice is to actually write the plain assert statements in the tests. The idea of the issue was to add a git workflow that runs the tests with the -O or -OO flag. pytest actually supports running the tests with these flags, since it automatically rewrites assert statements in the test directory at import time (i.e., before they are stripped from the optimization). assert statements in the main codebase will still be stripped, as expected.

I'm sorry if this was not clear from the issue I made. Would you be able to change this PR or (probably cleaner) open a new one that does not change the tests themselves, but rather the git workflows?

[arunkumargururaj07-star]

@LarsKue Thanks for the clarification. I’ve opened this new PR which only updates the CI workflow to run tests under -O / -OO, without modifying any test code.