Context, work, and explanation by @danielroe: #1532

We are thinking of improving (auto-generated) typed fetch. This requires adopting a new standard/reusable type utility for fetch, which @danielroe is working on. By using the new layer, we can improve performance and consistency and adopt it in several places instead of directly being in nitro core (benefiting nuxt, and in the next steps ofetch and h3 typed fetch support.)

Update: unjs/fetchdts is WIP project for better basis replacement.

Relevant linked issues: (some might be doable in next steps)

• $fetch return type is any if generics are passed to event handler #3507
• Expose a type infered from route response based on route name (NitroFetchRequest) and http method #3355
• $fetch infered type for Date is wrong #2689
• NitroRoute Serialize Type #2583
• Typescript shows server option doesn't exist for generic form of $fetch #1937
• Type inference and code execution interrupted by undocumented SerializeObject #1138
• $fetch type safety for query and body parameters #938
• Types for route inputs #841
• TS error Excessive stack depth comparing types when trying to wrap $fetch #470
• PUT, PATCH, and DELETE requests nuxt/nuxt#19077 (comment)