Async connection close handlers

[Rigidity]

Purpose:

This allows for databases queries to be executed inside of the disconnect handler of a peer (for example in the in-development #17012, which rewrites PeerSubscriptions to use an in-memory SQLite database).

Current Behavior:

The close handler interface is a regular function.

New Behavior:

It's now an async function, to support awaiting resources to be cleaned up.

Testing Notes:

[coveralls-official]

Pull Request Test Coverage Report for Build 7137015065

• 9 of 9 (100.0%) changed or added relevant lines in 6 files are covered.
• 13 unchanged lines in 8 files lost coverage.
• Overall coverage increased (+0.03%) to 90.267%

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Files with Coverage Reduction	New Missed Lines	%
chia/introducer/introducer.py	1	78.26%
chia/timelord/timelord_launcher.py	1	69.77%
tests/simulation/test_simulation.py	1	96.52%
chia/data_layer/data_layer.py	2	81.08%
chia/full_node/full_node_api.py	2	77.16%
chia/full_node/full_node.py	2	84.59%
chia/rpc/rpc_server.py	2	88.05%
chia/server/node_discovery.py	2	77.84%

Totals
Change from base Build 7133376678:	0.03%
Covered Lines:	93558
Relevant Lines:	103592

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💛 - Coveralls