fix: make orientation optional in async generate()

[davidhu2000]

Problem

Async text_to_video.generate() and ai_image_generator.generate() required orientation. It's deprecated in favor of aspect_ratio, and the sync generate() and both create() methods already treat it as optional.

Root cause

codemod/check_generate_create_sync.py compared only param names between generate() and create(). When the SDK generator made orientation optional in create() (#113, #114), the sync generate() got updated but the async one didn't. Since the name was still there, the check passed.

The same gap left other generate() params stale after later generator updates:

resource	sync	async
text_to_video	model, resolution	model, resolution, orientation
ai_image_generator	model, resolution	model, resolution, orientation
image_to_video	model, resolution	model, resolution
ai_image_editor	model, resolution	model, resolution
ai_video_editor	model	model
ai_image_upscaler	style (required, optional in create)	style

For example, generate(model="wan-3.0") or generate(model="krea-2") failed mypy even though create() accepts them.

Fix

• The codemod now also flags shared params whose type or default differs from create() (whitespace and trailing commas are normalized). --fix replaces the definition with the one from create() and keeps its position.
• The client changes come from python codemod/check_generate_create_sync.py --fix. Nothing was hand-edited, and a second --fix run produces no diff.
• Changed the CI PR comment to say "run --fix".
• Async README custom-docs examples for these two tools now use aspect_ratio="16:9" instead of orientation.

Verification

• python codemod/check_generate_create_sync.py: no issues
• pytest: 167 passed
• mypy magic_hour: no issues
• mypy on a README-style snippet that calls sync and async generate() without orientation: passes here, and fails on main with Missing named argument "orientation" (2 errors)

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