This PR addresses the confusion around WeChat Pay's new merchant transfer APIs that became mandatory for newly opened merchant accounts starting January 15, 2025.

Issue Summary

Users were unclear whether WxJava supports the "new version" of merchant transfer APIs that new merchants are required to use, as referenced in the official WeChat Pay documentation.

Key Findings

After thorough investigation, WxJava already fully supports the new merchant transfer APIs! The confusion arose because there are multiple transfer services:

What's Included in This PR

📚 Documentation

• NEW_TRANSFER_API_SUPPORT.md - Quick reference guide answering the user's question
• NEW_TRANSFER_API_USAGE.md - Comprehensive usage guide with examples

💻 Code Examples

• NewTransferApiExample.java - Complete working example demonstrating:
  • Single transfer creation (transferBills)
  • Transfer status queries (getBillsByOutBillNo, getBillsByTransferBillNo)
  • Transfer cancellation (transformBillsCancel)
  • Callback notification handling (parseTransferBillsNotifyResult)

For New Merchants

If you're a newly opened merchant account, use:

// Get the NEW transfer service (not MerchantTransferService)
TransferService transferService = wxPayService.getTransferService();

// Create transfer using new API
TransferBillsRequest request = TransferBillsRequest.newBuilder()
    .appid("your_appid")
    .outBillNo("T" + System.currentTimeMillis())
    .transferSceneId("1005")  // Required: Transfer scene ID
    .openid("user_openid")
    .transferAmount(100)      // Amount in cents
    .transferRemark("Commission payment")
    .build();

TransferBillsResult result = transferService.transferBills(request);

New API Advantages

• ✅ Single transfer support (vs batch-only in old API)
• ✅ Transfer cancellation capability
• ✅ Rich transfer scenarios (commission, rewards, etc.)
• ✅ Enhanced callback notifications
• ✅ Automatic RSA encryption for user names

All existing functionality remains unchanged - this PR only adds documentation and examples to clarify the already-existing support.

Fixes #3641.

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