update to syn 2.0

[Firestar99]

This was the last dependency in my project that still uses syn 1.0 :D

Note that within the repo there remains one usage of syn 1.0 on some targets (I assume windows only):

$ cargo tree -i syn@1 --target all
syn v1.0.109
├── com_macros v0.6.0 (proc-macro)
│   └── com v0.6.0
│       └── hassle-rs v0.11.0
│           └── wgpu-hal v22.0.0
│               ├── wgpu v22.1.0
│               │   └── example-runner-wgpu v0.0.0 (/rust-gpu/examples/runners/wgpu)
│               └── wgpu-core v22.1.0
│                   └── wgpu v22.1.0 (*)
└── com_macros_support v0.6.0
    └── com_macros v0.6.0 (proc-macro) (*)

[Firestar99]

these only exist to unify features across dependency trees

This made absolutely no difference in my testing with syn 2, A being with and B without this dependency. Tests were run by changing the line, cargo clean, cargo update and time cargo compiletest --target-env vulkan1.2 on a 6900HS (8/16 cores) with installed tools:

    native   spirv dep  real    user
A1  43.43s   9.35s      1m7     9m19    
A2  41.16s   8.79s      1m5     8m59    
B1  42.48s   8.84s      1m6     9m1     
B2  42.37s   9.00s      1m6     9m0    

[Firestar99]

There are other similar dependencies below I have not touched.