fix: remove startup/shutdown calls incompatible with Starlette 1.0

[megalaren]

Starlette 1.0 removed Router.startup() and Router.shutdown() methods.
The lifespan context (aenter/aexit) already handles the application lifecycle correctly.

[s3rius]

Can you bump minimum fastapi version to be the one where they deprecated the router.startup?

[megalaren]

This is actually a Starlette change, not FastAPI - those methods are missing from Starlette's router, which FastAPI inherits. So the constraint should be on the Starlette version, not FastAPI.

[vahidzhe]

Hi @s3rius

Just wanted to add a +1 on this PR — I'm also hitting the AttributeError: 'APIRouter' object has no attribute 'startup' issue after upgrading to FastAPI 0.128.3+ / Starlette 0.40.

The fix in this PR unblocks the problem. As a temporary workaround I'm currently pinning fastapi<0.128.3, but that's not sustainable long-term.

Is there anything blocking the merge? Happy to help test or add anything that would make this easier to land. 🙏