Feature Request: Support Square Brackets in Multipart Form Data for v3

[coderabbitai]

Description

Currently, Fiber supports square bracket notation in form data when using 'application/x-www-form-urlencoded' content type, but this functionality is not available for multipart form data. This feature request proposes adding support for square bracket notation in multipart form data for Fiber v3.

Current Behavior

• Square bracket notation works with 'application/x-www-form-urlencoded'
• Multipart form data does not support square bracket notation for nested structures

Desired Behavior

• Support square bracket notation in multipart form data
• Enable all features available in normal form data (including comma separation)
• Maintain ability to transfer binary data
• Allow parsing of nested structures like:

  text_prompts[0][text]: "value1"
  text_prompts[0][weight]: 0.7
  text_prompts[1][text]: "value2"
  text_prompts[1][weight]: -0.5
  

Use Cases

1. File uploads with complex metadata
2. Nested form structures with binary data
3. Arrays of objects in form data

References

• Original discussion: 🤗 [Question]: bodyParser nested with bracket notation #3223

/cc @ReneWerner87

[efectn]

Closing because the issue is duplication of #3224