feat: add withContext flag to getProgramAccounts (#1311)

## Summary

This was missing. When supplied, the RPC wraps the result in a context object.

Fixes #1285.

## Test Plan

```
pnpm test:live-with-test-validator
pnpm test:unit:node
```

packages/library-legacy/src/connection.ts

@@ -2685,8 +2685,16 @@ export type GetProgramAccountsConfig = {
   filters?: GetProgramAccountsFilter[];
   /** The minimum slot that the request can be evaluated at */
   minContextSlot?: number;
+  /** wrap the result in an RpcResponse JSON object */
+  withContext?: boolean;
 };
 
+export type GetProgramAccountsResponse = readonly Readonly<{
+  account: AccountInfo<Buffer>;
+  /** the account Pubkey as base-58 encoded string */
+  pubkey: PublicKey;
+}>[];
+
 /**
  * Configuration object for getParsedProgramAccounts
  */
@@ -3336,17 +3344,13 @@ export class Connection {
   /**
    * Fetch all the token accounts owned by the specified account
    *
-   * @return {Promise<RpcResponseAndContext<Array<{pubkey: PublicKey, account: AccountInfo<Buffer>}>>>}
+   * @return {Promise<RpcResponseAndContext<GetProgramAccountsResponse>}
    */
   async getTokenAccountsByOwner(
     ownerAddress: PublicKey,
     filter: TokenAccountsFilter,
     commitmentOrConfig?: Commitment | GetTokenAccountsByOwnerConfig,
-  ): Promise<
-    RpcResponseAndContext<
-      Array<{pubkey: PublicKey; account: AccountInfo<Buffer>}>
-    >
-  > {
+  ): Promise<RpcResponseAndContext<GetProgramAccountsResponse>> {
     const {commitment, config} =
       extractCommitmentFromConfig(commitmentOrConfig);
     let _args: any[] = [ownerAddress.toBase58()];
@@ -3621,10 +3625,24 @@ export class Connection {
    *
    * @return {Promise<Array<{pubkey: PublicKey, account: AccountInfo<Buffer>}>>}
    */
+  async getProgramAccounts(
+    programId: PublicKey,
+    configOrCommitment?: GetProgramAccountsConfig &
+      Readonly<{withContext: true}>,
+  ): Promise<RpcResponseAndContext<GetProgramAccountsResponse>>;
+  // eslint-disable-next-line no-dupe-class-members
   async getProgramAccounts(
     programId: PublicKey,
     configOrCommitment?: GetProgramAccountsConfig | Commitment,
-  ): Promise<Array<{pubkey: PublicKey; account: AccountInfo<Buffer>}>> {
+  ): Promise<GetProgramAccountsResponse>;
+  // eslint-disable-next-line no-dupe-class-members
+  async getProgramAccounts(
+    programId: PublicKey,
+    configOrCommitment?: GetProgramAccountsConfig | Commitment,
+  ): Promise<
+    | GetProgramAccountsResponse
+    | RpcResponseAndContext<GetProgramAccountsResponse>
+  > {
     const {commitment, config} =
       extractCommitmentFromConfig(configOrCommitment);
     const {encoding, ...configWithoutEncoding} = config || {};
@@ -3635,7 +3653,11 @@ export class Connection {
       configWithoutEncoding,
     );
     const unsafeRes = await this._rpcRequest('getProgramAccounts', args);
-    const res = create(unsafeRes, jsonRpcResult(array(KeyedAccountInfoResult)));
+    const baseSchema = array(KeyedAccountInfoResult);
+    const res =
+      configWithoutEncoding.withContext === true
+        ? create(unsafeRes, jsonRpcResultAndContext(baseSchema))
+        : create(unsafeRes, jsonRpcResult(baseSchema));
     if ('error' in res) {
       throw new SolanaJSONRPCError(
         res.error,

packages/library-legacy/test/connection.test.ts

@@ -749,6 +749,36 @@ describe('Connection', function () {
         });
       expect(programAccountsDoMatchFilter).to.have.length(2);
     }
+
+    {
+      await mockRpcResponse({
+        method: 'getProgramAccounts',
+        params: [
+          programId.publicKey.toBase58(),
+          {
+            commitment: 'confirmed',
+            withContext: true,
+          },
+        ],
+        value: {
+          context: {
+            slot: 11,
+          },
+          value: [],
+        },
+      });
+      const programAccountsWithContext = await connection.getProgramAccounts(
+        programId.publicKey,
+        {
+          commitment: 'confirmed',
+          withContext: true,
+        },
+      );
+      expect(programAccountsWithContext).to.have.nested.property(
+        'context.slot',
+      );
+      expect(programAccountsWithContext).to.have.property('value');
+    }
   }).timeout(30 * 1000);
 
   it('get balance', async () => {