Model call chains as an `AbstractTokenTarget` #248

Job	Run time
rustfmt	9s
lint	6s
test (ubuntu-latest, native)	6m 39s
test (ubuntu-20.04, native)	7m 36s
test (macos-latest, native)	9m 43s
test (ubuntu-20.04, aarch64-unknown-linux-gnu)	5m 1s
clippy	8m 29s
	37m 43s

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