Return an error instead of throwing on invalid UTF-8 in deserialisation helpers

[palas]

Context

deserialiseInput, deserialiseInputAnyOf and deserialiseAnyVerificationKeyBech32 (and thereby deserialiseAnyVerificationKey) used Text.decodeUtf8, which throws an impure exception when the input is not valid UTF-8. For example, deserialiseInput on the bytes "\xc3\x28" threw instead of returning Left InputInvalidError.

This PR switches them to Text.decodeUtf8' and treats invalid UTF-8 as a normal decoding failure.

How to trust this PR

• Invalid UTF-8 can never be valid Bech32, so mapping the decode failure to the existing "not valid Bech32" path (DeserialiseInputErrorFormatMismatch / Bech32DecodingError) does not change behaviour for any valid input.
• The three changed sites are mechanical: wrap the old code in the Right case of decodeUtf8'.

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated. See Running tests for more details
• Self-reviewed the diff
• Changelog fragment added in .changes/

[Copilot]

Pull request overview

This PR hardens Cardano API deserialisation helpers by avoiding Text.decodeUtf8’s impure exception on invalid UTF-8, ensuring these helpers return normal decoding errors instead of crashing.

Changes:

• Switched Bech32 deserialisation paths in deserialiseInput / deserialiseInputAnyOf to use Text.decodeUtf8' and treat invalid UTF-8 as a format mismatch.
• Updated deserialiseAnyVerificationKeyBech32 to avoid throwing on invalid UTF-8 and return a decoding error instead.
• Added a Herald changelog fragment documenting the bugfix.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
cardano-api/src/Cardano/Api/Serialise/DeserialiseAnyOf.hs	Avoids impure exceptions by using decodeUtf8' and mapping invalid UTF-8 to Bech32 format mismatch.
cardano-api/src/Cardano/Api/Key/Internal/SomeAddressVerificationKey.hs	Prevents invalid UTF-8 from throwing during Bech32 verification key deserialisation.
.changes/20260708_140000_cardano-api_pablo.lamela_nonthrowing_utf8_decode.yml	Changelog fragment describing the bugfix behavior change.

[Jimbo4350]

We shouldn't throw away the UnicodeException error. It needs to be rendered.