Update to syn 2.0

[mre]

Summary

It would be great if we could update syn to version 2.0 of the API as using syn 1.0 causes some downstream projects to have multiple versions of syn in the dependency tree at the moment. There have been some breaking API changes in syn 2.0, but nothing out of the ordinary. The only think I'm not 100% sure about is the error message for unknown shaku attributes; I can change that if needed.

Details

Update parse_terminated to include separator token parameter as required by syn 2.0 API changes. Replace Attribute field access with method calls:

• path -> path()
• tokens -> meta

Update attribute parsing to handle new Meta structure and provide better error messages based on attribute type (Path, List, NameValue).

These changes were needed to fix compilation errors after dependency update to syn 2.0.101.

Note that the compiler output changed; I updated it accordingly with TRYBUILD=overwrite cargo test -p shaku --test shaku_ui.

[AzureMarker]

Thanks for the PR, I will take a closer look when I get some time.

[AzureMarker]

Using Rust 1.87.0, I see some mismatches in the expected compiler output. You can update rust-toolchain with the new Rust version to see the changes. Interestingly, it now prints an internal compiler error in one of the tests:

error: internal compiler error: compiler/rustc_trait_selection/src/traits/normalize.rs:69:17: deeply_normalize should not be called with pending obligations: [
                                    Obligation(predicate=Binder { value: OutlivesPredicate(TestModule, 'static), bound_vars: [] }, depth=0),
                                ]

[AzureMarker]

I think you could replace the format call with "Unknown attribute" to keep this simple. The span should indicate to the user where the error is.