feat(cli): openapi directly to ir

[dsinghvi]

This PR started as a thought experiment -- what would it take to have Docs + SDKs share the OpenAPI parser and profit off of the same improvements.

In this PR, we've defined something that takes an OpenAPI spec and converts it to IR. It handles schema conversions, endpoint conversions (still multipart/streaming left to do), as well as converting servers.

The experiment proved a couple things:

1. The code is drastically simplified using this approach
2. This will save time for adding more features b/c you don't have to add it to the Fern Definition
3. It is eventually possible to delete the old OpenAPI parser b/c it will be feasible to make sure that the new parser respects all the feature flags of the old parser
4. Validation built in -- with an ErrorCollector interface its going to be so much easier to write validation rules and print them out for users (architecture suggested by alex)

[github-actions]

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