fix: use consistent u32 type for enum constants on Windows

[kajukitli]

bindgen generates C enums as i32 by default, but on Windows MSVC this can cause type mismatches when consuming code expects u32 constants.

Use EnumVariation::Consts to generate all enum constants as u32 for cross-platform consistency.

Fixes build errors like:

error[E0308]: mismatched types
   --> ext\node\ops\http2\types.rs:240:27
    |
240 |     nghttp2_hcat_request: ffi::NGHTTP2_HCAT_REQUEST,
    |                           ^^^^^^^^^^^^^^^^^^^^^^^^^ expected `u32`, found `i32`

See failing CI: https://github.com/denoland/deno/actions/runs/22631099295/job/65581121314?pr=32418