Fix store reconstruction

This MR aims to fix an issue when reconstructing a full storage after a snapshot import. Indeed, when importing a snapshot, we set the resulting context hash of the blocks of the floating block store to Context_hash.zero (this is fine as the context associated to it is not stored and cannot be queried as below the savepoint). However, after a reconstruction, these context hashes were not updated in the table maintained by the store, and thus, pointing to a wrong context hash (ie. Context_hash.zero).

This MR aims to update the resulting context hash of the blocks from the floating store while reconstructing them.

Manually testing the MR

Bake ~50 blocks, export a snapshot, import it with --reconstruct, query the metadata of blocks from 20 to 30. That should trigger the error without the patch.

Or run dune exec tezt/tests/main.exe -- --title "Alpha: storage reconstruction" on branch vicall@migrate_storage_reconstruction_test that is a new test that actually triggered the error

Closes

#4734 (closed)

Checklist

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