feat: add Custom provider (#181)

* feat: add Custom provider

* test: handle missing provider option in constructor

* feat: optional methods in `CustomProvider`

* docs: update README with Custom Provider

* fix: add CustomWallet to createWalletMap()

README.md

@@ -443,6 +443,77 @@ The following examples demonstrate how to use the `use-wallet` v3 library in var
 
 - [Vanilla TypeScript (Vite)](https://github.com/TxnLab/use-wallet/tree/v3/examples/vanilla-ts)
 
+## Custom Provider
+
+If you want to integrate a wallet provider that is not included in the library, or if your application requires any additional custom interactions, you can create a custom provider.
+
+1. Create a new class that implements the `CustomProvider` type
+
+```ts
+import { CustomProvider, WalletAccount } from '@txnlab/use-wallet' // Or any framework adapter
+
+class ExampleProvider implements CustomProvider {
+  /* Required */
+  async connect(args?: Record<string, any>): Promise<WalletAccount[]> {
+    // Must return an array of connected accounts
+    // Optional `args` parameter can be used to pass any additional configuration
+  }
+
+  /* Optional */
+  async disconnect(): Promise<void> {
+    // Disconnect from the wallet provider, if necessary
+  }
+
+  /* Optional */
+  async resumeSession(): Promise<WalletAccount[] | void> {
+    // Reconnect to the wallet provider when the app mounts, if necessary
+    // If an array of accounts is returned, they are checked against the stored accounts
+    // The stored accounts are updated if they differ
+  }
+
+  /* The two signing methods are optional, but you'll want to define at least one! */
+
+  async signTransactions(
+    txnGroup: algosdk.Transaction[] | algosdk.Transaction[][] | Uint8Array[] | Uint8Array[][],
+    indexesToSign?: number[],
+    returnGroup?: boolean
+  ): Promise<Uint8Array[]> {
+    // Sign transactions with the wallet
+    // Return signed transactions only or the original group if `returnGroup` is true
+  }
+
+  async transactionSigner(
+    txnGroup: algosdk.Transaction[],
+    indexesToSign: number[]
+  ): Promise<Uint8Array[]> {
+    // Sign an array of transaction objects with the wallet
+    // Return signed transactions only
+    // Compatible with algosdk's Atomic Transaction Composer
+  }
+}
+```
+
+2. Add the provider to the `WalletManager` configuration
+
+```ts
+const walletManager = new WalletManager({
+  wallets: [
+    // Include the custom provider in the wallets array
+    {
+      id: WalletId.CUSTOM,
+      options: {
+        provider: new ExampleProvider()
+      },
+      metadata: {
+        name: 'Example Wallet'
+        icon: 'data:image/svg+xml;base64,...'
+      }
+    }
+  ],
+  network: NetworkId.TESTNET
+})
+```
+
 ## WalletManager API
 
 The following API is exposed via the `WalletManager` class instance. The framework adapters abstract the `WalletManager` class and expose a similar API via the `useWallet` function.