feat: add Avalanche Fuji testnet support [APE-705]

[PoCk3T-SPAI]

What I did

As per https://docs.snowtrace.io/v/fuji-snowtrace, adding the Etherscan/Snowtrace API for Avalanche Fuji testnet in client.py

Checklist

• [X] Passes all linting checks (pre-commit and CI jobs)
• [X] New test cases have been added and are passing
• [X] Documentation has been updated
• [X] PR title follows Conventional Commit standard (will be automatically included in the changelog)

[PoCk3T-SPAI]

@fubuloubu humble contribution here I've identified 4 files where additions needed to be made to support the Fuji testnet of Avalanche Hope I didn't miss to update any other file Let me know your thoughts

[PoCk3T-SPAI]

@fubuloubu thanks for the prompt action; 2 CI/CD tests seem to have failed:

• Lint -> not sure what's the hold up, I followed the exact same syntax as the other ecosystems/chains listed and the lint test logs are not very descriptive
• Functional test -> it seems to be a test involving connecting to the ethereum mainnet, so out of scope for this PR What do you think? Any way you could force-merge this PR? Also happy to try and correct anything if needed?

[fubuloubu]

@fubuloubu thanks for the prompt action; 2 CI/CD tests seem to have failed:

• Lint -> not sure what's the hold up, I followed the exact same syntax as the other ecosystems/chains listed and the lint test logs are not very descriptive

To fix the lint issue, just run black or install pre-commit

[fubuloubu]

For the tests, you are right, they won't execute for you specifically because you don't have a Vess to our secrets. If you can run the new test locally (just grab an etherscan key) we can merge it with the lint fix and be on our way

[PoCk3T-SPAI]

Thanks @fubuloubu , done, hope it works!