Migrate tor_exit_nodes HTTP client to httpx (part of #1214)

[Prasad8830]

Description

This PR migrates only the Tor exit nodes cronjob HTTP call from requests to httpx, while preserving existing behaviour.

Scope is intentionally small and low risk:

• Updated greedybear/cronjobs/tor_exit_nodes.py to use httpx.get(...).
• Kept the same endpoint and timeout behaviour.
• Kept raise_for_status() handling and exception propagation behaviour.
• Updated Tor tests to patch/use the new HTTP client path and equivalent exception expectations.
• Added httpx dependency and updated lockfile.

This is an incremental step toward standardising HTTP usage in cron jobs, starting from a low-risk fetcher.

Related issues

• Standardize cronjob HTTP fetchers with a shared client wrapper #1214

Type of change

• 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).
• Chore (refactoring, dependency updates, CI/CD changes, code cleanup, docs-only changes).

Checklist

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Formalities

• I have read and understood the rules about how to Contribute to this project.
• I chose an appropriate title for the pull request in the form: <feature name>. Closes #999
• My branch is based on develop.
• The pull request is for the branch develop.
• I have reviewed and verified any LLM-generated code included in this PR.

Docs and tests

• I documented my code changes with docstrings and/or comments.
• I have checked if my changes affect user-facing behaviour that is described in the docs. If so, I also created a pull request in the docs repository.
• Linter (Ruff) gave 0 errors. If you have correctly installed pre-commit, it runs these checks and makes these adjustments on your behalf.
• I have added tests for the feature/bug I solved.
• All the tests gave 0 errors.

GUI changes

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• I have provided a screenshot of the result in the PR.
• I have created new frontend tests for the new component or updated existing ones.

[regulartim]

I'll convert this to a draft, as it is not ready for review yet.

[regulartim]

Succeeded by #1253 and #1254