verification-client should ensure test cases are parseable at startup

[dansanduleac]

What happened?

Test case values are parsed into their endpoint's expected conjure type only when the tests are executed.

What did you want to happen?

• verification-client should parse test cases once, at startup, to make sure that they are all parseable. This is what verification-server does (implemented in server: Verify all test cases parse as expected #70).
• a unit test should be added to ensure the generated test cases can be parsed.