This PR fixes staging stables handling by view building coordinator in case of intra-node tablet migration or tablet merge.
To support tablet merge, the worker stores the sstables grouped only be `table_id`, instead of `(table_id, last_token)` pair.
There shouldn't be that many staging sstables, so selecting relevant for each `process_staging` task is fine.
For the intra-node migration support, the patch adds methods to load migrated sstables on the destination shard and to cleanup them on source shard.
The patch should be backported to 2025.4
Fixes https://github.com/scylladb/scylladb/issues/26244Closesscylladb/scylladb#26454
* github.com:scylladb/scylladb:
service/storage_service: migrate staging sstables in view building worker during intra-node migration
db/view/view_building_worker: support sstables intra-node migration
db/view_building_worker: fix indent
db/view/view_building_worker: don't organize staging sstables by last token
f0039381d2