survey: add tree stats #676

Job	Run time
config	3s
fuzz smoke test	34s
win+VS build	0s
linux32 (daald/ubuntu32:xenial)	2m 6s
linux-musl (alpine)	1m 34s
pedantic (fedora)	1m 38s
documentation	1m 19s
linux-asan-ubsan (ubuntu-latest)	2m 2s
linux-gcc (ubuntu-20.04)	1m 9s
linux-gcc-default (ubuntu-latest)	1m 12s
linux-leaks (ubuntu-latest)	44s
linux-reftable (ubuntu-latest)	1m 20s
linux-reftable-leaks (ubuntu-latest)	48s
linux-sha256 (ubuntu-latest)	1m 23s
linux-TEST-vars (ubuntu-20.04)	1m 9s
win+VS test	0s
osx-clang (macos-13)	44s
osx-gcc (macos-13)	1m 28s
osx-reftable (macos-13)	1m 2s
sparse	2m 21s
static-analysis	4m 7s
win build	2m 37s
win test	0s
	29m 20s

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