add generated media download timeouts

[zhonggang666]

What this PR does / why we need it?

Adds explicit timeouts and HTTP status checks when generated media workflow nodes download remote image/video URLs.

Closes #6370.

Summary of your change

• Adds a generated media download timeout constant.
• Uses requests.get(..., timeout=...) for generated remote media URLs.
• Calls raise_for_status() before saving the downloaded media bytes.

Please indicate you've done the following:

• Made sure tests are passing and test coverage is added if needed.
• Made sure commit message follow the rule of Conventional Commits specification.
• Considered the docs impact and opened a new docs issue or PR with docs changes if needed.

Validation:

• python -m py_compile apps/application/flow/step_node/image_generate_step_node/impl/base_image_generate_node.py apps/application/flow/step_node/text_to_video_step_node/impl/base_text_to_video_node.py apps/application/flow/step_node/image_to_video_step_node/impl/base_image_to_video_node.py
• git diff --check

[liuruibin]

没有修改计划