## Context
Taking a slightly different approach to [this
PR](https://github.com/supabase/supabase/pull/43370)
Original problem was that if you opened some folders while in a bucket
and then switched to a different bucket, the folder UI will persists
(folders from Bucket A will render when landing on Bucket B)
## Changes involved
- Shift `StorageExplorerStateContextProvider` into `[bucketId].tsx]`
instead of `ProjectContext`
- The valtio store here only applies for the storage explorer so having
it so high in the project's context was unnecessary
- This also just implies that the valtio store will automatically reset
whenever the bucket changes
- Simplify storage explorer valtio store by initializing the store with
the bucket
- We'll initialize the selected bucket with the store now (Same as
previous PR)
- Removes unnecessary `setSelectedBucket` method which required a
separate `useEffect` in `StorageExplorer.tsx`
## To test
- [ ] Verify that the original is resolved
- [ ] General smoke test of the storage explorer - i've also re-added
the e2e test that Gildas wrote up in his PR