concoredocker.py has no test coverage

[avinxshKD]

The test_concore.py only covers concore.py but there's nothing for concoredocker.py.

Looking at the code, concoredocker.py has its own implementations of read(), write(), initval(), unchanged() etc that are different from concore.py - uses absolute paths /in and /out instead of relative, slightly different error handling, etc.

These differences could easily break in Docker containers without anyone noticing since there's no tests running against the docker variant.

so should probably add at least basic tests for:

• safe_literal_eval()

• read() and write() with mocked file paths

• initval() parsing

• unchanged() state tracking

Would also catch the kind of drift that happens when someone updates concore.py but forgets concoredocker.py.

[avinxshKD]

@pradeeban what do you think, let me know if this seems useful? Added a pr