[bindings] When running npm run build:update-bindings, misuse of FFI types from Rust causes warnings

[Fizzixnerd]

when run from nix develop o1js, there appears to be misuse/exporting of Rust-specific types in plonk_wasm.

Since the types are stored in ark_ff, it may be possible to avoid the warning by using a pointer instead of the actual field struct.

Feel free to close if this is just noise, but I thought I'd add it for completeness.

... <SNIP> ...

warning: unused manifest key: target.wasm32-unknown-unknown.rustflags
   Compiling plonk_wasm v0.1.0 (/home/fizzixnerd/src/o1js/_build/default/src/mina/src/lib/crypto/kimchi_bindings/wasm)
warning: `extern` fn uses type `ark_ff::Fp<MontBackend<FqConfig, 4>, 4>`, which is not FFI-safe
   --> src/projective.rs:130:9
    |
130 |         WasmPastaFp,
    |         ^^^^^^^^^^^ not FFI-safe
    |
    = help: consider adding a `#[repr(C)]` or `#[repr(transparent)]` attribute to this struct
    = note: this struct has unspecified layout
    = note: `#[warn(improper_ctypes_definitions)]` on by default

warning: `extern` fn uses type `ark_ff::Fp<MontBackend<FrConfig, 4>, 4>`, which is not FFI-safe
   --> src/projective.rs:128:9
    |
128 |         WasmPastaFq,
    |         ^^^^^^^^^^^ not FFI-safe
    |
    = help: consider adding a `#[repr(C)]` or `#[repr(transparent)]` attribute to this struct
    = note: this struct has unspecified layout

warning: `extern` fn uses type `ark_ff::Fp<MontBackend<FrConfig, 4>, 4>`, which is not FFI-safe
   --> src/projective.rs:149:9
    |
149 |         WasmPastaFq,
    |         ^^^^^^^^^^^ not FFI-safe
    |
    = help: consider adding a `#[repr(C)]` or `#[repr(transparent)]` attribute to this struct
    = note: this struct has unspecified layout

warning: `extern` fn uses type `ark_ff::Fp<MontBackend<FqConfig, 4>, 4>`, which is not FFI-safe
   --> src/projective.rs:147:9
    |
147 |         WasmPastaFp,
    |         ^^^^^^^^^^^ not FFI-safe
    |
    = help: consider adding a `#[repr(C)]` or `#[repr(transparent)]` attribute to this struct
    = note: this struct has unspecified layout

warning: `plonk_wasm` (lib) generated 4 warnings

... <SNIP> ...