feat: Implement ProtocolApprovalsManager

I decided to make ProtocolApprovalsManager public method sync not to propagate asynceness early on onto the rest of the code. If later we decide that it is better to have this async, it should be easier to make that change than the opposite one.

--- don't change below this line ---
ENG-4064 Took 24 minutes

src/encoding/evm/swap_encoder/encoders.rs

@@ -53,17 +53,10 @@ impl SwapEncoder for BalancerV2SwapEncoder {
         encoding_context: EncodingContext,
     ) -> Result<Vec<u8>, EncodingError> {
         let token_approvals_manager = ProtocolApprovalsManager::new();
-        let runtime = tokio::runtime::Handle::try_current()
-            .is_err()
-            .then(|| tokio::runtime::Runtime::new().unwrap())
-            .unwrap();
         let token = bytes_to_address(&swap.token_in)?;
         let router_address = bytes_to_address(&encoding_context.address_for_approvals)?;
-        let approval_needed = runtime.block_on(async {
-            token_approvals_manager
-                .approval_needed(token, self.vault_address, router_address)
-                .await
-        });
+        let approval_needed =
+            token_approvals_manager.approval_needed(token, router_address, self.vault_address)?;
         // should we return gas estimation here too?? if there is an approval needed, gas will be
         // higher.
         let args = (