fix(eth-sender): Check the existance of eth txs before getting the correct block for statistics (#4359)

## What ❔

Execute light query for checking the existance of eth tx with necessary
type. If it exists, we can execute statistics query. Which are more
expensive

## Why ❔

For majority of l2 blocks, the eth transcations doesn't exist. So it
leads to extremely expensive queries.

## Is this a breaking change?
- [ ] Yes
- [ ] No

## Operational changes
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## Checklist

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- [ ] PR title corresponds to the body of PR (we generate changelog
entries from PRs).
- [ ] Tests for the changes have been added / updated.
- [ ] Documentation comments have been added / updated.
- [ ] Code has been formatted via `zkstack dev fmt` and `zkstack dev
lint`.

Signed-off-by: Danil <[email protected]>

Author: Deniallugo

core/lib/dal/.sqlx/query-b882586949146ef1e7867b133ad6cb00d88e73118347e1f33c041ef27bf62ebc.json

@@ -209,7 +209,7 @@ impl EthSenderDal<'_, '_> {
         Ok(count.try_into().unwrap())
     }
 
-    pub async fn get_eth_all_blocks_stat(&mut self) -> sqlx::Result<BlocksEthSenderStats> {
+    pub async fn get_eth_all_blocks_stat(&mut self) -> DalResult<BlocksEthSenderStats> {
         struct EthTxRow {
             number: i64,
             confirmed: bool,
@@ -224,6 +224,24 @@ impl EthSenderDal<'_, '_> {
 
         let mut stats = BlocksEthSenderStats::default();
         for &tx_type in TX_TYPES {
+            // Execute cheap query to check if there are any transactions of this type.
+            let eth_txs_type_exist: bool = sqlx::query!(
+                r#"
+                SELECT EXISTS(
+                    SELECT 1
+                    FROM eth_txs WHERE tx_type = $1
+                )
+                "#,
+                tx_type.to_string()
+            )
+            .instrument("get_existence_of_eth_txs_by_type")
+            .fetch_one(self.storage)
+            .await?
+            .exists
+            .unwrap_or_default();
+            if !eth_txs_type_exist {
+                continue;
+            }
             let mut tx_rows = vec![];
             for confirmed in [true, false] {
                 let query = match_query_as!(
@@ -253,7 +271,12 @@ impl EthSenderDal<'_, '_> {
                         ),
                     }
                 );
-                tx_rows.extend(query.fetch_all(self.storage.conn()).await?);
+                tx_rows.extend(
+                    query
+                        .instrument("get_eth_blocks_stat")
+                        .fetch_all(self.storage)
+                        .await?,
+                );
             }
 
             for row in tx_rows {