Support backtracking and `Checkpoint`s across nodes #348

Job	Run time
Check	23s
Check doc links	22s
Clippy	28s
Miri ubuntu-latest	1m 58s
Miri windows-latest	2m 45s
Rustfmt	11s
Miri macos-latest	1m 24s
address sanitizer	58s
Test stable on ubuntu-latest	1m 40s
memory sanitizer	1m 2s
Test nightly on ubuntu-latest	1m 37s
thread sanitizer	1m 0s
Test stable on windows-latest	3m 37s
leak sanitizer	56s
Test nightly on windows-latest	3m 7s
Test stable on macos-latest	1m 23s
Test nightly on macos-latest	2m 29s
	25m 20s

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