Fix async method naming: move Async suffix to end per .NET conventions

[Copilot]

Source generator was placing Async suffix in the middle of async string method names (ReadConfigAsyncAsString) instead of at the end (ReadConfigAsStringAsync), violating .NET naming conventions.

Changes

• Source Generator: Fixed method name generation to place Async suffix at end for string methods

  • Introduced named variables for method names to improve consistency
  • Byte array async methods were already correct

• Examples & Documentation: Updated method calls and examples to match new naming pattern

Before/After

// Before (incorrect)
string config = await R.ReadConfigAsyncAsString();

// After (correct)
string config = await R.ReadConfigAsStringAsync();

All generated methods for resource "config":

Task<byte[]> ReadConfigAsync()                      // byte[] async (unchanged)
Task<string> ReadConfigAsStringAsync()              // string async (fixed)
Task<string> ReadConfigAsStringAsync(Encoding enc)  // string async with encoding (fixed)
byte[] ReadConfig()                                 // byte[] sync
string ReadConfigAsString()                         // string sync
Stream GetConfigStream()                            // stream

Original prompt

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This section details on the original issue you should resolve

<issue_title>SG 生成的异步方法名称需要优化，确保 Async 在方法名的最后。</issue_title>
<issue_description>假如有资源 Config.txt ，目前生成的读取代码是：R.ReadConfigAsyncAsString() 这种方法命名并不友好，应该改为 R.ReadConfigAsStringAsync() 。

需要修改SG项目的实现，并更新文档（README 等）。</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes SG 生成的异步方法名称需要优化，确保 Async 在方法名的最后。 #43

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