data: define interface for `read_last_scalars` #11018

Job	Run time
lint-misc	21s
lint-python-flake8 (3.9)	24s
build-data-server-pip (native, ubuntu-20.04, 1.65.0)	2m 15s
lint-frontend	2m 0s
lint-python-flake8 (3.10)	31s
build-data-server-pip (native, macos-12, 1.65.0)	3m 55s
lint-python-yaml-docs	35s
lint-python-flake8 (3.11)	27s
build-data-server-pip (universal, ubuntu-20.04, 1.65.0)	13s
lint-rust (1.65.0, 0.16.1)	54s
build (tf, 3.9)	19m 14s
build (notf, 3.9)	10m 35s
	41m 24s

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