Support older versions of python in gradio 5

[not-lain]

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Is your feature request related to a problem? Please describe.
Gradio 5 does not work on older versions of Python
context : #9463 (comment)

Describe the solution you'd like

to support versions that are using 3.9

from __future__ import annotations

at the top of each file that uses any typing features.

Although some resources that I checked are conflicting if either this fixes support for only 3.9 or (3.9 backwards till 3.7), I am certain that it would fix any problems with 3.9 in all cases.

Additional context
sources :

• https://docs.python.org/3/whatsnew/3.7.html#pep-563-postponed-evaluation-of-annotations
• https://stackoverflow.com/questions/61544854/from-future-import-annotations
• https://discuss.python.org/t/what-within-future-made-list-str-start-working-on-3-7/5428

[pngwn]

There is more to supporting 3.9 in gradio than just this, there are other places where supporting older versions added complexity or gave a worse experience.

Dropping support for older versions of Python was intentional in this release as it frees us up robust modern syntax in the future. Updating to 3.10 isn't an unreasonable ask in 2024.