Add `last_value` to `ScalarTimeSeries` interface. #10808

Job	Run time
lint-frontend	2m 15s
lint-frontend	2m 15s
lint-frontend	2m 15s
lint-python-flake8 (3.9)	27s
lint-python-flake8 (3.9)	27s
lint-python-flake8 (3.9)	27s
lint-python-flake8 (3.10)	18s
lint-python-flake8 (3.10)	18s
lint-python-flake8 (3.10)	18s
lint-python-flake8 (3.11)	21s
lint-python-flake8 (3.11)	21s
lint-python-flake8 (3.11)	21s
lint-misc	19s
lint-misc	19s
lint-misc	19s
build-data-server-pip (native, ubuntu-22.04, 1.65.0)	1m 53s
build-data-server-pip (native, ubuntu-22.04, 1.65.0)	1m 53s
build-data-server-pip (native, ubuntu-22.04, 1.65.0)	1m 53s
build-data-server-pip (native, macos-12, 1.65.0)	4m 2s
build-data-server-pip (native, macos-12, 1.65.0)	4m 2s
build-data-server-pip (native, macos-12, 1.65.0)	4m 2s
build-data-server-pip (universal, ubuntu-22.04, 1.65.0)	18s
build-data-server-pip (universal, ubuntu-22.04, 1.65.0)	18s
build-data-server-pip (universal, ubuntu-22.04, 1.65.0)	18s
lint-python-yaml-docs	35s
lint-python-yaml-docs	35s
lint-python-yaml-docs	35s
lint-rust (1.65.0, 0.16.1)	36s
lint-rust (1.65.0, 0.16.1)	36s
lint-rust (1.65.0, 0.16.1)	36s
build (tf, 3.9)	15m 58s
build (tf, 3.9)	15m 58s
build (tf, 3.9)	15m 58s
build (notf, 3.9)	10m 57s
build (notf, 3.9)	9m 27s
build (notf, 3.9)	6m 9s
	1h 47m 39s

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