fix(coprocessor): add missing indexes for selecting allowed handles when tx unsent

Author: antoniupop

coprocessor/fhevm-engine/db-migration/migrations/20251230155309_improve_sns_and_txsend_select_indexing.sql

@@ -0,0 +1,18 @@
+--- Improve indexing for SNS worker selection queries
+
+CREATE INDEX IF NOT EXISTS idx_pbs_computations_pending_created_at
+ON pbs_computations (created_at, handle)
+WHERE is_completed = FALSE;
+
+CREATE INDEX IF NOT EXISTS idx_ciphertexts_handle_not_null
+ON ciphertexts (handle)
+WHERE ciphertext IS NOT NULL;
+
+--- Improve indexing for Tx-sender selection queries
+
+CREATE INDEX IF NOT EXISTS idx_allowed_txn_is_sent
+ON allowed_handles (txn_is_sent);
+
+CREATE INDEX IF NOT EXISTS idx_allowed_txn_retries
+ON allowed_handles (txn_limited_retries_count)
+WHERE txn_is_sent = false;