[docs][data] Documentation code coverage

[richardliaw]

Doctest infrastructure stopped working at some point, and we only caught it recently when Ed refactored some of the code. There are several failures across our documentation:

ray/doc/BUILD

Lines 455 to 465 in d87d2fd

	# These tests are currently failing.
	"source/data/loading-data.rst",
	"source/data/data-internals.rst",
	"source/data/inspecting-data.rst",
	"source/data/loading-data.rst",
	"source/data/performance-tips.rst",
	"source/data/saving-data.rst",
	"source/data/working-with-images.rst",
	"source/data/working-with-llms.rst",
	"source/data/working-with-pytorch.rst",
	],

Originally posted by @bveeramani in #52534

• "source/data/loading-data.rst",
• "source/data/data-internals.rst",
• "source/data/inspecting-data.rst",
• "source/data/loading-data.rst",
• "source/data/performance-tips.rst",
• "source/data/saving-data.rst" ([Data][Docs] Code snippet in "Saving Data" doesn't work #52534)
• "source/data/working-with-images.rst",
• "source/data/working-with-llms.rst",
• "source/data/working-with-pytorch.rst",

[Bye-legumes]

let me and @zhaoch23 verify some of them

[zhaoch23]

"source/data/loading-data.rst" is failing because of this issue: #48689