Fix upload multipart headers and encode invoke URL segments

[Chandraveersingh1717]

This PR fixes two request construction issues in the API client.

1. upload()
   Forward FormData headers (fd.getHeaders()) when sending multipart
   requests with axios. Without these headers the multipart boundary
   may be missing, which can break /api/package/create in Node.

2. invoke()
   Encode dynamic URL path segments (prefix, suffix, version, name)
   using encodeURIComponent() to correctly handle special characters
   such as spaces or slashes.

These fixes prevent malformed requests and improve client reliability.

Tests:

• Added unit tests to verify multipart headers are forwarded.
• Added tests to ensure invoke() correctly encodes URL segments.