fix(tee): correct previous fix for race condition in batch locking

Commit a7dc0ed (PR #3342) was supposed
to fix a race condition in batch locking by introducing SQL row-locking,
but it didn't work as expected. Now we are switching back to
coarser-grained table-level locking as [originally suggested][1] by
Harald. The original fix was hard to test unless deployed to `stage` due
to the undeterministic nature of the problem, so we needed to merge it
to the `main` branch to properly test it.

[1]: #3342 (comment)

core/lib/dal/src/tee_proof_generation_dal.rs

@@ -66,10 +66,16 @@ impl TeeProofGenerationDal<'_, '_> {
         let min_batch_number = i64::from(min_batch_number.0);
         let mut transaction = self.storage.start_transaction().await?;
 
-        // Lock rows in the proof_generation_details table to prevent race conditions. The
-        // tee_proof_generation_details table does not have corresponding entries yet if this is the
-        // first time the query is invoked for a batch. Locking rows in proof_generation_details
-        // ensures that two different TEE prover instances will not try to prove the same batch.
+        // Lock the entire tee_proof_generation_details table in EXCLUSIVE mode to prevent race
+        // conditions. Locking the table ensures that two different TEE prover instances will not
+        // try to prove the same batch.
+        sqlx::query("LOCK TABLE tee_proof_generation_details IN EXCLUSIVE MODE")
+            .instrument("lock_batch_for_proving#lock_table")
+            .execute(&mut transaction)
+            .await?;
+
+        // The tee_proof_generation_details table does not have corresponding entries yet if this is
+        // the first time the query is invoked for a batch.
         let batch_number = sqlx::query!(
             r#"
             SELECT
@@ -95,8 +101,6 @@ impl TeeProofGenerationDal<'_, '_> {
                     )
                 )
             LIMIT 1
-            FOR UPDATE OF p
-            SKIP LOCKED
             "#,
             tee_type.to_string(),
             TeeProofGenerationJobStatus::PickedByProver.to_string(),