[chore] Remove VCR as production dependency

[nwithan8]

Description

Rather than storing a global VCR (requiring EasyVCR to be a production dependency), we now store a global Function that accepts a string and returns an HttpsUrlConnection. This function is set by the test suite to use the configured VCR, but this means that EasyVCR does not leave the test suite.

Should close #265

Testing

• All unit tests pass, cassettes replayed as normal after rebuild (suggests that function is working as expected, no impact on flow).
• Can confirm that EasyVCR is no longer downloaded during build/install process (accidentally kept an import during testing and compiler correctly complains about a missing import)

Pull Request Type

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

• [x] 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)
• [x] Improvement (fixing a typo, updating readme, renaming a variable name, etc)

[nwithan8]

praise: This is awesome, nice work!

question: before merging, can we re-record one cassette locally to ensure that a fresh HTTP request gets made and comment back on the findings? No need to commit the cassette

Yes, cassettes are recorded and replayed as expected: