Deep merges two OpenAPI/Swagger definition maps.

Rules:

• paths are merged per path + method
• components are deeply merged
• tags are concatenated (deduped by name)
• servers are concatenated (deduped by url)
• everything else: right side overrides left

Converts an OpenAPI/Swagger paths definition into a list of Phoenix-compatible routes.

This function extracts HTTP operations from the OpenAPI document and transforms them into Openapi.Route structs that can later be used to generate Phoenix router entries or dispatch metadata.