Fix missing cosmology.compat.camb package dependency

[arthurmloureiro]

Summary

cosmology.compat.camb was used within the package but was not declared as a dependency in pyproject.toml,
causing import errors for users who installed glass.ext.camb without it.

Closes #21

Changes

• Added cosmology.compat.camb to the dependencies list in pyproject.toml so it is automatically installed
  alongside the package.
• Also added it to the test optional dependencies for completeness.
• Bumped requires-python from >=3.6 to >=3.10 to reflect actual runtime requirements.
• Added a unit test (tests/test_cosmology_compat.py) that verifies cosmology.compat.camb.Cosmology can be
  instantiated from CAMB results.

Testing

The new test checks that a Cosmology object can be constructed from a CAMB background run and that the
resulting H0 value is correct.

[arthurmloureiro]

@glass-dev/developers :)