Adopt PEP 621, move metadata into `pyproject.toml` #447

Job	Run time
test-postgres (9.5)	3m 7s
test-postgres (9.6)	2m 42s
test-postgres (10)	3m 16s
test-postgres (11)	3m 7s
test-postgres (12)	3m 34s
test-postgres (13)	3m 22s
test-postgres (14)	2m 44s
test-postgres (15)	2m 37s
test-platforms (3.8, ubuntu-latest, asyncio)	2m 14s
test-platforms (3.8, ubuntu-latest, uvloop)	2m 31s
test-platforms (3.8, macos-latest, asyncio)	4m 42s
test-platforms (3.8, macos-latest, uvloop)	2m 51s
test-platforms (3.8, windows-latest, asyncio)	7m 13s
test-platforms (3.9, ubuntu-latest, asyncio)	2m 3s
test-platforms (3.9, ubuntu-latest, uvloop)	2m 23s
test-platforms (3.9, macos-latest, asyncio)	5m 20s
test-platforms (3.9, macos-latest, uvloop)	2m 59s
test-platforms (3.9, windows-latest, asyncio)	5m 7s
test-platforms (3.10, ubuntu-latest, asyncio)	2m 0s
test-platforms (3.10, ubuntu-latest, uvloop)	2m 6s
test-platforms (3.10, macos-latest, asyncio)	3m 23s
test-platforms (3.10, macos-latest, uvloop)	3m 7s
test-platforms (3.10, windows-latest, asyncio)	5m 32s
test-platforms (3.11, ubuntu-latest, asyncio)	2m 14s
test-platforms (3.11, ubuntu-latest, uvloop)	1m 56s
test-platforms (3.11, macos-latest, asyncio)	3m 20s
test-platforms (3.11, macos-latest, uvloop)	6m 16s
test-platforms (3.11, windows-latest, asyncio)	5m 39s
Regression Tests	1s
	1h 37m 26s

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