Update SQL types, improve SQL *big.Int

- In SQL Tables, set rollup_vars.forge_l1_timeout to BIGINT (instead of BYTEA)
- In "bigint" encoding/decoding used with meddler, store the *big.Int as raw
  bytes, instead of base64 to be more space efficient

db/migrations/0001.sql

@@ -526,7 +526,7 @@ FOR EACH ROW EXECUTE PROCEDURE forge_l1_user_txs();
 CREATE TABLE rollup_vars (
     eth_block_num BIGINT PRIMARY KEY REFERENCES block (eth_block_num) ON DELETE CASCADE,
     fee_add_token BYTEA NOT NULL,
-    forge_l1_timeout BYTEA NOT NULL,
+    forge_l1_timeout BIGINT NOT NULL,
     withdrawal_delay BIGINT NOT NULL,
     buckets BYTEA
 );