Issue 303 gdal failed import

[e-lo]

What existing problem does the pull request solve and why should we include it?

The purpose of this PR is to not require GDAL to be installed in testing environment.

GDAL is required to be imported in order to use a full-fledged Emme environment and it tends to need to be imported first.

Other (interdependent) issues addressed in order to get tests passing:

1. Added a ctramp_context to check if ctramp installed before trying to run those tests
2. Moved Union City session-level fixture to conftest for greater availability
3. Has inro_context return "inro" or "mock" so that we can use that value to understand which part of tests we can run
4. For parts of tests which require full inro context, have them return at the point where they need it
5. Require mkdocstrings >0.18 which uses griffe instead of tk to do the code inspection and update some identifier references

What is the testing plan?

Demonstrate the code is solid by discussing how results are verified and covered by tests

• Run GH Action Locally using act -j build
• Run tests locally using pytest
• Run pre-commit locally using pre-commit run --all-files
• Run Tests locally using a machine with Emme installed

Code formatting

Code should be PEP8 compliant before merging by running a package like black

• Code linted

Applicable Issues

Please do not create a Pull Request without creating an issue first.

Closes #93

[i-am-sijia]

This PR needs to be tested with Emme before merging.