Fixes #617

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Problem

After upgrading from ruby-openai 8.1 to 8.2, users encountered an ArgumentError when using streaming with Faraday 2.1.0:

ArgumentError: wrong number of arguments (given 2, expected 3)

The error occurs because Faraday 2.1.0 calls the on_data callback with only 2 arguments (chunk, size), but the new Stream#call method expects 3 arguments (chunk, _bytes, env).

Root Cause

In version 8.2.0, streaming functionality was refactored from an inline Proc in HTTP#to_json_stream to a dedicatedStream class (PR #589). This introduced a breaking change:

Before 8.2.0 (worked fine):

• Used a Proc: proc do |chunk, _bytes, env|
• Ruby Procs are flexible with argument counts - when called with fewer arguments, missing parameters become nil
• Faraday calling with 2 arguments worked without errors

After 8.2.0 (breaks):

• Uses a method: def call(chunk, _bytes, env)
• Ruby methods strictly enforce argument counts
• Faraday calling with 2 arguments raises ArgumentError

Faraday's Behavior

In faraday-net_http v2.1.0, the callback is invoked with only 2 parameters:

# https://github.com/lostisland/faraday-net_http/blob/v2.1.0/lib/faraday/adapter/net_http.rb#L112
env[:request].on_data.call(chunk, size)

Solution

Make the env parameter optional with a default value of nil:

def call(chunk, _bytes, env = nil)

This maintains backward compatibility with different Faraday versions while preserving the same functionality.