fix(stream): EventSource ignores use_file_output=False

[devteamaegis]

What's broken

EventSource silently ignores use_file_output=False. The constructor assigns the flag with use_file_output or True, but False or True evaluates to True in Python, so the caller's intent is lost:

source = EventSource(client, response, use_file_output=False)
print(source.use_file_output)  # True — should be False

Output tokens are still run through transform_output even when the caller explicitly opted out.

Why it happens

The line self.use_file_output = use_file_output or True is meant to default to True when None is passed, but it clobbers a deliberate False as well since Python's or operator returns the right-hand side for any falsy left-hand side.

Fix

Replace the boolean-or default with an explicit None check:

self.use_file_output = use_file_output if use_file_output is not None else True