Parse #[error] format arguments and fmt handlers

[RAprogramm]

Summary

• allow #[error("…")] to parse trailing format arguments into FormatArg metadata
• recognise #[error(fmt = )] handlers, capturing their path and guarding against duplicate fmt specs
• surface clearer diagnostics when unsupported argument combinations are used and add trybuild coverage
• bump crate versions and update changelog/readme entries

Testing

• cargo +nightly fmt --
• RUSTUP_TOOLCHAIN=1.90.0 cargo clippy -- -D warnings
• RUSTUP_TOOLCHAIN=1.90.0 cargo build --all-targets
• RUSTUP_TOOLCHAIN=1.90.0 cargo test --all
• RUSTUP_TOOLCHAIN=1.90.0 cargo doc --no-deps
• cargo deny check
• cargo audit

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https://chatgpt.com/codex/tasks/task_e_68cd5180b2bc832ba3440e7714561b93