Testing process is not documented and possibly broken

[Vlad-Shcherbina]

I was trying to make a minor change but couldn't get the tests running. There are no testing instructions in the README or similar places.

The CI config suggests cargo test --all-features, but this didn't work locally for me. Also noticed the CI builds are consistently failing.

Could you please document how to test this project locally during development? Adding this to the README would make it easier for potential contributors.

[oscartbeaumont]

Since we broke all of the logic out of being a single crate to multiple all of the tests have been a pretty big mess. This was a shortcut we did so we could focus on the main refactor.

What needs to happen:

• Typescript tests broken out of 'specta-test' crate onto the 'specta-typescript' crate.
• Introduce new tests on the 'DataType' structure included as tests on the 'specta' crate.
• Drop the 'specta-test' crate

Right now the tests can be run like 'cargo test --all-features -p specta-test' but I'm fairly sure not all of them pass because for example the Zod exporter is still a work in progress.