chore(rustup): add rust-toolchain.toml config #973

Job	Run time
dco / check	4s
reuse / test	12s
e2e-test / e2e-test	5m 43s
warmup-caches / build	1m 9s
multi-platform / windows-latest / test	7m 16s
test / test	1m 6s
check / clippy	1m 12s
test / coverage	3m 4s
check / fmt	21s
check / msrv / 1.78	40s
check / features	3m 29s
check / minimal-versions	1m 12s
check / stable / for-publish	1m 12s
check / doc	41s
check / semver	0s
	27m 21s

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