Rust: Manual reimplementation of C unions and layout testing

[Igor Korotin <igor.korotin.linux@gmail.com>]

Hello all,

As you might know, I'm working on the Rust side of the I2C subsystem, 
and currently looking into representing `struct i2c_algorithm`.

In C, this struct contains two anonymous unions for callbacks.
bindgen generates rather awkward names for them, which makes the Rust
bindings less readable and less stable.

I'm considering declaring this structure manually in i2c.rs, effectively
copying the layout that bindgen would generate but renaming the union
fields for clarity. To avoid accidental ABI drift, I could add 
compile-time assertions to ensure the Rust and C layouts remain compatible.

Would that be an acceptable approach?
Any thoughts or preferences on how such layout checks should be done 
in-tree?

Best regards,
Igor Korotin