Expose APIs for working with transaction proposals

Closes Electric-Coin-Company/zcash-swift-wallet-sdk#1204.

CHANGELOG.md

@@ -25,6 +25,27 @@ The old `Synchronizer.sendToAddress` and `Synchronizer.shieldFunds` APIs have be
 deprecated, and will be removed in 2.1.0 (which will create multiple transactions
 at once for some recipients).
 
+# Unreleased
+
+## Changed
+
+### [#1186] Enable ZIP 317 fees
+- The SDK now generates transactions using [ZIP 317](https://zips.z.cash/zip-0317) fees,
+  instead of a fixed fee of 10,000 Zatoshi. Use `Proposal.totalFeeRequired` to check the
+  total fee for a transfer before creating it.
+
+## Added
+
+### [#1204] Expose APIs for working with transaction proposals
+New `Synchronizer` APIs that enable constructing a proposal for transferring or
+shielding funds, and then creating transactions from a proposal. The intermediate
+proposal can be used to determine the required fee, before committing to producing
+transactions.
+
+The old `Synchronizer.sendToAddress` and `Synchronizer.shieldFunds` APIs have been
+deprecated, and will be removed in 2.1.0 (which will create multiple transactions
+at once for some recipients).
+
 # 2.0.10 - 2024-02-12
 
 ## Added

Sources/ZcashLightClientKit/Synchronizer/CombineSDKSynchronizer.swift

@@ -80,6 +80,36 @@ extension CombineSDKSynchronizer: CombineSynchronizer {
         }
     }
 
+    public func proposeShielding(
+        accountIndex: Int,
+        shieldingThreshold: Zatoshi,
+        memo: Memo
+    ) -> SinglePublisher<Proposal, Error> {
+        AsyncToCombineGateway.executeThrowingAction() {
+            try await self.synchronizer.proposeShielding(accountIndex: accountIndex, shieldingThreshold: shieldingThreshold, memo: memo)
+        }
+    }
+
+    public func createProposedTransactions(
+        proposal: Proposal,
+        spendingKey: UnifiedSpendingKey
+    ) -> SinglePublisher<AsyncThrowingStream<TransactionSubmitResult, Error>, Error> {
+        AsyncToCombineGateway.executeThrowingAction() {
+            try await self.synchronizer.createProposedTransactions(proposal: proposal, spendingKey: spendingKey)
+        }
+    }
+
+    public func proposeTransfer(
+        accountIndex: Int,
+        recipient: Recipient,
+        amount: Zatoshi,
+        memo: Memo?
+    ) -> SinglePublisher<Proposal, Error> {
+        AsyncToCombineGateway.executeThrowingAction() {
+            try await self.synchronizer.proposeTransfer(accountIndex: accountIndex, recipient: recipient, amount: amount, memo: memo)
+        }
+    }
+
     public func proposeShielding(
         accountIndex: Int,
         shieldingThreshold: Zatoshi,