feat: add direct write

[xuxiao415]

Add direct write for Writer

This PR adds direct write capability to the Writer struct, allowing data to be written directly to the underlying io.Writer without buffering. This feature provides performance benefits by reducing memory copies and enabling real-time output for streaming scenarios.

The main changes include:

• Added WithDirectWrite(direct bool) option to enable/disable direct write mode
• Added directWrite field to Writer struct to track the current mode
• Modified all write methods (WriteBool, WriteInt, WriteLong, WriteFloat, WriteDouble, WriteBytes, WriteString) to support direct writing
• Enhanced Flush method to handle direct write mode efficiently
• Updated WriteBlockCB to properly handle direct write mode transitions
• Added comprehensive test coverage for direct write functionality

Key Benefits:

• Performance improvement: Eliminates buffer-to-output copying in direct write mode
• Memory efficiency: Reduces memory usage when direct write is enabled
• Real-time output: Data is written immediately, suitable for streaming applications
• Backward compatibility: Default behavior remains unchanged (buffered mode)

Usage:

// Enable direct write mode
writer := NewWriter(output, 1024, WithDirectWrite(true))

// Default buffered mode (existing behavior)
writer := NewWriter(output, 1024)

How did I test it?

I thoroughly tested the direct write functionality through multiple approaches:

1. Unit Tests

• Added 9 new test functions specifically for direct write mode:

  • TestWriter_WriteBool_DirectWrite
  • TestWriter_WriteInt_DirectWrite
  • TestWriter_WriteLong_DirectWrite
  • TestWriter_WriteFloat_DirectWrite
  • TestWriter_WriteDouble_DirectWrite
  • TestWriter_WriteBytes_DirectWrite
  • TestWriter_WriteString_DirectWrite
  • TestWriter_WriteBlockHeader_DirectWrite
  • TestWriter_WriteBlockCB_DirectWrite

• All tests verify that:

  • Buffer remains empty in direct write mode
  • Data is written directly to output
  • No data loss occurs during mode transitions

2. Existing Test Suite

• Ran all existing Writer tests to ensure no regression
• All 33 Writer tests pass successfully
• Verified that original buffered mode behavior is unchanged

3. Edge Case Testing

• Tested WriteBlockCB with direct write mode to ensure proper data handling
• Verified error handling in direct write mode
• Confirmed Flush optimization works correctly

4. Integration Testing

• Tested with various data types and sizes
• Verified compatibility with different io.Writer implementations
• Confirmed proper memory management and buffer reuse

5. Performance Verification

• Confirmed that direct write mode eliminates unnecessary buffer operations
• Verified that Flush method correctly handles empty buffers in direct write mode
• Tested memory reuse behavior to ensure no memory leaks

All tests pass successfully, confirming that the direct write functionality works correctly while maintaining full backward compatibility with existing code.

[nrwiersma]

Please cleanup the code. Comments need to be in english for this to be considered.