refactor(anta.tests): Nicer result failure messages BFD & Connectivity test module

[vitthalmagadum]

Description

Updated failure messages for following tests

1. test_bfd.py
   1. VerifyBFDPeersRegProtocols

2. test_connectivity.py
   1. VerifyReachability
   2. VerifyLLDPNeighbors

Fixes #587

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• 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
• New and existing unit tests pass locally with my changes (tox -e testenv)

[codspeed-hq]

CodSpeed Performance Report

Merging #1029 will not alter performance

_{Comparing vitthalmagadum:issue_587_connectivity_and_bfd (c14222f) with main (f0ae643)}

Summary

✅ 22 untouched benchmarks

[geetanjalimanegslab]

LGTM

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[carl-baillargeon]

LGTM.