fix: limit gas usage by sequencer tx (#13)

Limit the gas usage by sequencer sponsored transactions. The limit was
chosen arbitrarily

crates/wallet/src/lib.rs

@@ -138,6 +138,11 @@ pub enum OdysseyWalletError {
     /// This is likely an internal error, as most of the request is built by the sequencer.
     #[error("invalid tx request")]
     InvalidTransactionRequest,
+    /// The request was estimated to consume too much gas.
+    ///
+    /// The gas usage by each request is limited to counteract draining the sequencers funds.
+    #[error("request would use too much gas")]
+    GasEstimateTooHigh,
     /// An internal error occurred.
     #[error("internal error")]
     InternalError,
@@ -267,6 +272,9 @@ where
             EthCall::estimate_gas_at(&self.inner.eth_api, request.clone(), BlockId::latest(), None)
                 .await
                 .map_err(Into::into)?;
+        if estimate >= U256::from(150_000) {
+            return Err(OdysseyWalletError::GasEstimateTooHigh.into());
+        }
         request = request.gas_limit(estimate.to());
 
         // set gas fees