Fixed drag-circle task name + Use gymnasium API in tests.

[ppasupat]

Description

• Consolidated drag-item and drag-circle task names.
• Made the tests use gymnasium.make(...) instead of MiniWoBEnvironment(...).
• Turned off threading in the Selenium instance handler (used for running multiple Selenium instances, but we removed that functionality).

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• I have run the pre-commit checks with pre-commit run --all-files (see CONTRIBUTING.md instructions to set it up)
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes