Refactor: Use derive Default attribute instead of impl blocks

[leighmcculloch]

What

Replace the hand-written impl Default blocks on the CLI's InputFormat and OutputFormat enums with #[derive(Default)] and a #[default] variant attribute.

Why

Nine copies of a six-line impl Default express nothing the derive can't, and the default variant is easier to spot on the variant itself than in a separate impl below the enum.

Broken out of #560, which requires the change to handle a newer version of clippy. We can make the change now though as its a good non-functional refactor.

Known limitations

N/A

[Copilot]

Pull request overview

Replaces manual CLI format defaults with Rust’s derived Default implementation while preserving behavior.

Changes:

• Adds Default derives to input/output format enums.
• Marks the existing default variants with #[default].
• Removes 12 redundant manual implementations.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/cli/types/schema.rs	Derives the schema output default.
src/cli/types/schema_files.rs	Derives the schema-files output default.
src/cli/types/list.rs	Derives the list output default.
src/cli/guess.rs	Derives guess input and output defaults.
src/cli/generate/default.rs	Derives the default-generator output default.
src/cli/generate/arbitrary.rs	Derives the arbitrary-generator output default.
src/cli/encode.rs	Derives encode input and output defaults.
src/cli/decode.rs	Derives decode input and output defaults.
src/cli/compare.rs	Derives the compare input default.

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