Graceful shutdown logic partially broken after moving to `uvloop`

[droserasprout]

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Restore shutdown() from there: https://github.com/dipdup-io/dipdup/pull/1074/files#diff-e360e59f12a611d858c3b5cdfbeb8c9a250aacfd77fabb17f789f12a49a12001

Looks like uvloop behaves differently from asyncio loop in processing signals.

Steps to reproduce:

Send SIGINT to running indexer

What did you expect to happen:

All asyncio tasks cancelled, indexer silently stops, no reports in Sentry

What actually happened:

Environment

• Python version:
• DipDup version or commit hash: 8.5.0
• Database engine version:
• Hasura version:
• Are you in docker?
• Can you reproduce this issue on next?