fix: handle arrays properly in FormData

[omarmciver]

Description

This PR fixes an issue with FormData handling when arrays are involved, particularly for multi-file uploads.

The Problem

When an API endpoint accepts an array of files (or any array in FormData), the current implementation incorrectly converts the entire array to a string representation instead of properly appending each item individually to the FormData object.

Example scenario:

// API expects multiple file attachments
const files = [file1, file2, file3];
api.uploadMultiple({ files });

// Current behavior: FormData contains
// "files" => "[object File],[object File],[object File]" ❌

// Expected behavior: FormData should contain
// "files" => file1
// "files" => file2  
// "files" => file3 ✅

The Solution

This fix modifies the FormData content formatter to:

1. Detect when a property value is an array
2. Iterate through each item in the array
3. Properly append each item individually to FormData
4. Preserve the correct handling of Blob/File types vs other data types

Changes Made

• Updated templates/base/http-clients/fetch-http-client.ejs to handle arrays in FormData
• Added test fixture formdata-arrays.json to verify the fix
• All existing tests pass with updated snapshots

Use Cases

This fix is essential for:

• Multi-file upload endpoints
• Batch document processing APIs
• Any FormData field that accepts multiple values
• Services handling attachments (e.g., agreement management systems)

Testing

• ✅ All existing tests pass
• ✅ Snapshots updated to reflect the new array handling
• ✅ Added test fixture for multi-file upload scenario

Backwards Compatibility

This change is fully backwards compatible:

• Single values continue to work as before
• Arrays are now handled correctly instead of being stringified
• No breaking changes to the API

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Latest commit: 6e854b8

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[lc-soft]

String type values do not need to be converted to strings again, as this can result in double quotes at both ends of the string

[lc-soft]

I have tried modifying it this way and it can solve the problem.

formData.append(
  key,
  formItem instanceof Blob || typeof formItem === "string"
    ? formItem
    : JSON.stringify(formItem)
);

[lc-soft]

Since File extends Blob, you can simplify this check to just formItem instanceof Blob.

[omarmciver]

@lc-soft Thank you for the excellent code review! I've implemented both of your suggestions:

1. ✅ Simplified Blob check: Removed redundant File instanceof check since File extends Blob
2. ✅ Fixed string handling: Added explicit string type check to prevent double-stringification

The updated code now correctly handles:

• Blob/File types: Passed directly to FormData ✅
• Strings: Passed directly without JSON.stringify ✅
• Objects/Arrays: JSON.stringify applied ✅
• Numbers/Booleans: JSON.stringify applied ✅

Most importantly: The original bug fix (handling arrays in FormData for multi-file uploads) still works perfectly! 🎉

Changes pushed in commit b9da1cd

[omarmciver]

✅ Tests fixed!

Updated all test snapshots to reflect the refactored FormData handling. All 133 tests now passing.

Changes in commit 6e854b8:

• 28 snapshot files updated
• 114 snapshots refreshed
• All tests green ✅