This PR addresses two related issues in our task system:
1. Prepares for asynchronous resource cleanup by converting release_resources() to a coroutine. This refactoring enables future improvements in how we handle resource cleanup.
2. Fixes a cross-shard resource cleanup issue in the SSTable loader where destruction of per-shard progress elements could trigger "shared_ptr accessed on non-owner cpu" errors in multi-shard environments. The fix uses coroutines to ensure resources are released on their owner shards.
Fixes#22759
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this change addresses a regression introduced by d815d7013c, which is contained by 2025.1 and master branches. so it should be backported to 2025.1 branch.
Closesscylladb/scylladb#22791
* github.com:scylladb/scylladb:
sstable_loader: fix cross-shard resource cleanup in download_task_impl
tasks: make release_resources() a coroutine
1b44861e8f