Fix encoding::EncodingOverride when not enabling query_encoding feature

[nox]

This is a breaking change, but at the same this fixes a bug that can cause build issues anyway, so I'm on the fence this time.

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This change is 

[nox]

Cc @emilio @SimonSapin @Eijebong because we all have opinions about semver.

[nox]

This may be a good opportunity to define the missing methods that don't depend on the encoding crate for when the feature is not enabled.

[SimonSapin]

What’s the build issue?

Note that the encoding module is not public and its content not re-exported. Now that pub(crate) is a thing, we should use it for its contents to make that more clear.

[nox]

@SimonSapin Ooooooooh. Sorry for the brainfart. 'Tis no public, so there is no problem.