* refactor: move streaming helper to `streaming/sse.ts`
* feat: add streamSSE's export in streaming handler
* feat: move `stream` and `streamText` to streaming helper
* chore: add deprecated expression for `c.stream` and `c.streamText`
* fix: use `stream` helper in streamSSE
* refactor: move `streamText` to `text.ts`
* test: add some case to `stream` and `streamText`
* test: refactor `streamSSE` case for uniformity
* chore: denoify
* fix: update jsdoc's deprecated description, simplify `c.stream` and `c.streamText`
* fix: match the header notation with that of `streamSSE
* chore: denoify
* refactor: remove unnecesary export
