Add a client for BankForks (#10728)

Also:
* Use BanksClient in solana-tokens

banks-interface/src/lib.rs

@@ -0,0 +1,49 @@
+use serde::{Deserialize, Serialize};
+use solana_sdk::{
+    account::Account,
+    clock::Slot,
+    commitment_config::CommitmentLevel,
+    fee_calculator::FeeCalculator,
+    hash::Hash,
+    pubkey::Pubkey,
+    signature::Signature,
+    transaction::{self, Transaction, TransactionError},
+};
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+pub struct TransactionStatus {
+    pub slot: Slot,
+    pub confirmations: Option<usize>, // None = rooted
+    pub err: Option<TransactionError>,
+}
+
+#[tarpc::service]
+pub trait Banks {
+    async fn send_transaction_with_context(transaction: Transaction);
+    async fn get_fees_with_commitment_and_context(
+        commitment: CommitmentLevel,
+    ) -> (FeeCalculator, Hash, Slot);
+    async fn get_transaction_status_with_context(signature: Signature)
+        -> Option<TransactionStatus>;
+    async fn get_slot_with_context(commitment: CommitmentLevel) -> Slot;
+    async fn process_transaction_with_commitment_and_context(
+        transaction: Transaction,
+        commitment: CommitmentLevel,
+    ) -> Option<transaction::Result<()>>;
+    async fn get_account_with_commitment_and_context(
+        address: Pubkey,
+        commitment: CommitmentLevel,
+    ) -> Option<Account>;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use tarpc::{client, transport};
+
+    #[test]
+    fn test_banks_client_new() {
+        let (client_transport, _server_transport) = transport::channel::unbounded();
+        BanksClient::new(client::Config::default(), client_transport);
+    }
+}