sparse_mmap: remove C code and add SAFETY comments #2064

Job	Run time
build mdbook guide	2m 20s
build artifacts [x64-linux]	6m 1s
build and check docs [x64-windows]	9m 55s
build openhcl [aarch64-linux]	5m 28s
build openhcl [x64-linux]	7m 55s
verify openhcl binary size [x64]	6m 31s
clippy [windows], unit tests [x64-windows]	11m 31s
clippy [linux, macos], unit tests [x64-linux]	8m 5s
unit tests [aarch64-windows]	8m 18s
clippy [linux-musl, misc nostd], unit tests [x64-linux-musl]	7m 10s
build and check docs [x64-linux]	2m 55s
test flowey local backend	3m 12s
xtask fmt (linux)	2m 27s
build artifacts (not for VMM tests) [aarch64-windows]	5m 52s
build artifacts (for VMM tests) [aarch64-windows]	9m 36s
build artifacts (for VMM tests) [x64-windows]	9m 51s
build artifacts (not for VMM tests) [x64-windows]	5m 55s
build artifacts [aarch64-linux]	5m 19s
xtask fmt (windows)	6m 44s
run vmm-tests [aarch64-windows]	6m 23s
run vmm-tests [x64-linux]	9m 14s
run vmm-tests [x64-windows-intel]	10m 42s
run vmm-tests [x64-windows-amd]	12m 49s
openvmm checkin gates	6s
	2h 44m 19s

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