actix-settings: v0.7.0

• The ApplySettings trait now includes a type parameter, allowing multiple types to be implemented per configuration target.
• Implement ApplySettings for ActixSettings.
• BasicSettings::from_default_template() is now infallible.
• Rename AtError => Error.
• Remove AtResult type alias.
• Update toml dependency to 0.8.
• Remove ioe dependency; std::io::Error is now used directly.
• Remove Clone implementation for Error.
• Implement Display for Error.
• Implement std's Error for Error.
• Minimum supported Rust version (MSRV) is now 1.68.