Add AuthkestraIntegration derive macro for simplified state integration

[onelrian]

Summary

Introduces #[derive(AuthkestraIntegration)] macro to eliminate FromRef boilerplate when integrating Authkestra with custom Axum application state.

Problem

Integrating Authkestra with custom Axum AppState currently requires implementing 4 manual FromRef traits, creating approximately 30 lines of boilerplate code per integration.

Solution

Created authkestra-axum-macros crate providing a derive macro that automatically generates all required FromRef implementations.

Before

#[derive(Clone)]
struct AppState<S, T> {
    auth: Authkestra<S, T>,
    db_pool: Arc<PgPool>,
}

// 30+ lines of manual FromRef implementations
impl<S: Clone, T: Clone> FromRef<AppState<S, T>> for Authkestra<S, T> { ... }
impl<S, T> FromRef<AppState<S, T>> for Result<Arc<dyn SessionStore>, ...> { ... }
// ... 2 more implementations

After

use authkestra_axum::AuthkestraIntegration;

#[derive(Clone, AuthkestraIntegration)]
struct AppState<S, T> {
    #[authkestra]
    auth: Authkestra<S, T>,
    db_pool: Arc<PgPool>,
}

Changes

• Created authkestra-axum-macros proc-macro crate
• Implemented AuthkestraIntegration derive macro with compile-time validation
• Added optional macros feature to authkestra-axum
• Updated axum_credentials example demonstrating simplified integration
• Added comprehensive documentation and migration guide

Impact

• Reduces integration boilerplate by 90%
• Backward compatible with existing AuthkestraState usage
• Type-safe with compile-time validation
• Optional feature flag, no forced dependency

Testing

• All workspace tests pass
• Examples compile and run correctly
• Backward compatibility verified

Closes #2

[marcjazz]

• Rename the new crate from authkestra-axum-macros to authkestra-macros: This will help support other integrations macros in the features.
• Add the renamed authkestra-macros with axum feature to the authkestra-axum cargo.toml. Make it available by default.
• Rename AuthkestraIntegration to AuthkestraFromRef

[marcjazz]

This code is now irrelevant and should be deleted.

[onelrian]

The AuthkestraState struct and its FromRef implementations serve a different purpose than the new AuthkestraFromRef macro:

• AuthkestraState: Simple wrapper for users who only need Authkestra with no custom state fields
• AuthkestraFromRef macro: For custom state structs with additional fields (e.g., db_pool, custom services)

They're complementary patterns, not replacements. Removing AuthkestraState would:

• Break 3 existing examples (axum_oauth.rs, oidc_generic.rs, axum_spa_jwt.rs)
• Force all users to use the macro even for simple cases
• Be a breaking change

So , should I still delete it ?

[marcjazz]

Use the macros crate to implement the AuthkestraState internal and existing example shall remain untouched.

[marcjazz]

Use the macros crate to implement the AuthkestraState internal and existing example shall remain untouched.

[onelrian]

Fixed the requested changes:

• Refactored AuthkestraState to use the AuthkestraFromRef macro internally
• Fixed all clippy warnings across the codebase (30+ uninlined_format_args warnings)