easypost client

[Justintime50]

Description

Adds the new EasyPostClient object allowing for thread-safety. The repo is in a hybrid stage where the old way of doing things still exists but we're able to introduce the new approach as well. In follow-up PRs, I'll add the remaining services/models, eventually remove the old code for each, then cleanup the requester and all related code for actually making requests. This allows the current test suite to remain for now while letting us switch over to the new approach.

Testing

• [x] Added new tests for the Client object
• [x] Updated syntax for address tests

Pull Request Type

Please select the option(s) that are relevant to this PR.

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [x] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Improvement (fixing a typo, updating readme, renaming a variable name, etc)

[wildsparx]

The underscore solution sounds fine to me. It's a convention that you can expect the caller to respect.