chore: use requestAirdrop to fund e2e accounts

@willemneal [pointed out](stellar/stellar-docs#1101 (review))
that it's a bit of a bummer to create accounts with a pure-SDK interface
just to revert to `fetch` and a hard-coded Friendbot URL in order to
fund that account.

This uses `rpc.Server#requestAirdrop` to do the funding.

I find the name of this method a bit unexpected! I wonder if the
language here has evolved since the method was first added.

test/e2e/src/util.js

@@ -1,5 +1,5 @@
 const { spawnSync } = require("node:child_process");
-const { contract, Keypair } = require("../../../lib");
+const { contract, Keypair, rpc } = require("../../../lib");
 const path = require("node:path");
 
 /*
@@ -18,12 +18,12 @@ module.exports.run = run;
 
 const stellar = "./target/bin/stellar";
 const basePath = path.resolve(
-  `${__dirname}/../test-contracts/target/wasm32-unknown-unknown/release`,
+  `${__dirname}/../test-contracts/target/wasm32-unknown-unknown/release`
 );
 const contracts = {
   customTypes: {
     hash: run(
-      `${stellar} contract install --wasm ${basePath}/custom_types.wasm`,
+      `${stellar} contract install --wasm ${basePath}/custom_types.wasm`
     ).stdout,
     path: `${basePath}/custom_types.wasm`,
   },
@@ -47,13 +47,13 @@ const contracts = {
   },
   needsSignature: {
     hash: run(
-      `${stellar} contract install --wasm ${basePath}/needs_a_signature.wasm`,
+      `${stellar} contract install --wasm ${basePath}/needs_a_signature.wasm`
     ).stdout,
     path: `${basePath}/needs_a_signature.wasm`,
   },
   doesSigning: {
     hash: run(
-      `${stellar} contract install --wasm ${basePath}/this_one_signs.wasm`,
+      `${stellar} contract install --wasm ${basePath}/this_one_signs.wasm`
     ).stdout,
     path: `${basePath}/this_one_signs.wasm`,
   },
@@ -67,17 +67,13 @@ const networkPassphrase =
   process.env.SOROBAN_NETWORK_PASSPHRASE ??
   "Standalone Network ; February 2017";
 module.exports.networkPassphrase = networkPassphrase;
-const friendbotUrl =
-  process.env.SOROBAN_FRIENDBOT_URL ?? "http://localhost:8000/friendbot";
-module.exports.friendbotUrl = friendbotUrl;
 
 async function generateFundedKeypair() {
   const keypair = Keypair.random();
-  await fetch(
-    friendbotUrl === "https://friendbot.stellar.org"
-      ? `${friendbotUrl}/?addr=${keypair.publicKey()}`
-      : `${friendbotUrl}/friendbot?addr=${keypair.publicKey()}`,
-  );
+  const server = new rpc.Server(rpcUrl, {
+    allowHttp: rpcUrl.startsWith("http://") ?? false,
+  });
+  await server.requestAirdrop(keypair.publicKey());
   return keypair;
 }
 module.exports.generateFundedKeypair = generateFundedKeypair;
@@ -123,7 +119,7 @@ async function clientFor(name, { keypair, contractId } = {}) {
       wasmHash: wasmHash,
       publicKey: internalKeypair.publicKey(),
       ...signer,
-    },
+    }
   );
   const { result: client } = await deploy.signAndSend();
 
@@ -139,7 +135,7 @@ async function installContract(name, { keypair } = {}) {
   if (!contracts[name]) {
     throw new Error(
       `Contract ${name} not found. ` +
-        `Pick one of: ${Object.keys(contracts).join(", ")}`,
+        `Pick one of: ${Object.keys(contracts).join(", ")}`
     );
   }
 
@@ -148,7 +144,7 @@ async function installContract(name, { keypair } = {}) {
   let wasmHash = contracts[name].hash;
   if (!wasmHash) {
     wasmHash = run(
-      `${stellar} contract install --wasm ${contracts[name].path}`,
+      `${stellar} contract install --wasm ${contracts[name].path}`
     ).stdout;
   }
   return { keypair: internalKeypair, wasmHash };