Header values are URI encoded

Header values are URI-encoded by swift-openapi-generator. This is incorrect eg. for `Cache-Control` headers where translating `max-cache=3600` to `max-cache%3D3600` produces an invalid cache-control header.

Start by locating where generated HTTP header values are URI-encoded and reproduce the Cache-Control example from the issue. Done means header values such as max-cache=3600 remain unencoded and produce valid Cache-Control headers; add or update coverage if the relevant tests are found.

Written by the indexing model from the issue text.