What

This MR fixes some ambiguities in the docstrings of data-encoding.

Why

So that odoc does not fail once we plug data-encoding in !12004 (merged)

By running make -C doc odoc-lite in !12004 (merged) and checking the errors.

It's a bit tricky because for some reason make @data-encoding/doc does nothing. Just check the CI of !12004 (merged) I guess: https://gitlab.com/tezos/tezos/-/pipelines/1246618410

Document the interface of any function added or modified (see the coding guidelines)
Document any change to the user interface, including configuration parameters (see node configuration)
Provide automatic testing (see the testing guide).
For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
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