docs(blob): update godoc comments to better match what Get and GetProof actually do #8118

Job	Run time
Markdown Lint	6s
setup	2s
yamllint	13s
hadolint / hadolint	7s
go-ci / Setup	1s
go-ci / Lint	2m 44s
go-ci / Go Mod Tidy Check	17s
go-ci / Unit Tests Coverage (ubuntu-latest)	3m 48s
go-ci / Unit Tests Coverage (macos-14)	2m 48s
go-ci / Integration Tests / Integration Tests Blob	2m 52s
go-ci / Integration Tests / Da Tests Sync	2m 36s
go-ci / Integration Tests / Integration Tests API	2m 58s
go-ci / Integration Tests / Integration Tests Fraud	2m 48s
go-ci / Integration Tests / Integration Tests p2p	2m 43s
go-ci / Integration Tests / Integration Tests ND	2m 54s
go-ci / Integration Tests / Integration Tests Reconstruction	2m 47s
go-ci / Integration Tests / Integration Tests Sync	3m 7s
version_bump	3s
goreleaser	0s
upload-docs	0s
	32m 54s

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