fix: block signature saving (#867)

Description
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Signature was not saved in the DB. So whenever the block was not send
immediately but via sync there was no signature and it failed.

Motivation and Context
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How Has This Been Tested?
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What process can a PR reviewer use to test or verify this change?
---


Breaking Changes
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- [x] None
- [ ] Requires data directory to be deleted
- [ ] Other - Please specify

dan_layer/state_store_sqlite/src/writer.rs

@@ -191,6 +191,7 @@ impl<TAddr: NodeAddressable> StateStoreWriteTransaction for SqliteStateStoreWrit
             blocks::qc_id.eq(serialize_hex(block.justify().id())),
             blocks::is_dummy.eq(block.is_dummy()),
             blocks::is_processed.eq(block.is_processed()),
+            blocks::signature.eq(block.get_signature().map(serialize_json).transpose()?),
             blocks::foreign_indexes.eq(serialize_json(block.get_foreign_indexes())?),
         );