feat(anta.tests): Optimize VerifyRoutingTableEntry by quering all routes for a vrf.

[dlobato]

Description

Reduce number of commands executed on VerifyRoutingTableEntry by querying all routes of a vrf in one go.

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my code
• [x] I have run pre-commit for code linting and typing (pre-commit run)
• [ ] I have made corresponding changes to the documentation
• [ ] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes (tox -e testenv)