[dart-dio] Fix json_serializable response for type:string format:binary

[matthewnitschke-wk]

Summary

Using the dart-dio generator against a response of type:string, format:binary, would result in a MultipartFile return type. This causes the deserialize function to fail.

This PR takes inspiration from the built_value serialization method by treating response file types as Uint8List

Closes #20682

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• [x] Run the following to build the project and update samples:

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  (For Windows users, please run the script in WSL) Commit all changed files. This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master. These must match the expectations made by your contribution. You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*. IMPORTANT: Do NOT purge/delete any folders/files (e.g. tests) when regenerating the samples as manually written tests may be removed.
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@jaumard (2018/09) @josh-burton (2019/12) @amondnet (2019/12) @sbu-WBT (2020/12) @kuhnroyal (2020/12) @agilob (2020/12) @ahmednfwela (2021/08)

[matthewnitschke-wk]

@wing328 Ended up creating a specific test case for this to prevent effecting non-dart-dio generators: bin/configs/dart-dio-binary-response.yaml

Can you approve the workflow run so we can see if tests pass?

[matthewnitschke-wk]

@jaumard (2018/09) @josh-burton (2019/12) @amondnet (2019/12) @sbu-WBT (2020/12) @kuhnroyal (2020/12) @agilob (2020/12) @ahmednfwela (2021/08)

Any thoughts?

[wing328]

@matthewnitschke-wk thanks again for the PR

is it correct to say that you've tested this fix locally with your use cases and it's working as expected?

[matthewnitschke-wk]

@matthewnitschke-wk thanks again for the PR

is it correct to say that you've tested this fix locally with your use cases and it's working as expected?

@wing328 Correct, I've validated that the specific combination of type:string + format:binary response works locally

[wing328]

ok. let's give it a try

[wing328]

thanks again for the PR which has been merged