fix: enable wasip2 feature for wasm32-wasip2 target

[brooksmtownsend]

Fixes #958

Hi! 👋🏻

wasm32-wasip2 is a tier 3 target for compilation in Rust, and has landed in Rust nightly.

I'm working on seanmonstar/reqwest#2290 and hoping to add wasm32-wasip2 support for a crate or two that depend on url, the compiler error currently when building shows:

➜ cargo +nightly build --target wasm32-wasip2
warning: /Users/brooks/github.com/servo/rust-url/url_debug_tests/Cargo.toml: no edition set: defaulting to the 2015 edition while the latest is 2021
   Compiling url v2.5.2 (/Users/brooks/github.com/servo/rust-url/url)
error[E0658]: use of unstable library feature 'wasip2'
    --> url/src/lib.rs:2836:9
     |
2836 |     use std::os::wasi::prelude::OsStrExt;
     |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
     |
     = help: add `#![feature(wasip2)]` to the crate attributes to enable
     = note: this compiler was built on 2024-08-06; consider upgrading it if it is out of date

error[E0658]: use of unstable library feature 'wasip2'
    --> url/src/lib.rs:2939:9
     |
2939 |     use std::os::wasi::prelude::OsStrExt;
     |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
     |
     = help: add `#![feature(wasip2)]` to the crate attributes to enable
     = note: this compiler was built on 2024-08-06; consider upgrading it if it is out of date

For more information about this error, try `rustc --explain E0658`.
error: could not compile `url` (lib) due to 2 previous errors

After this PR:

 ➜ cargo +nightly build --target wasm32-wasip2                                                                      
warning: /Users/brooks/github.com/servo/rust-url/url_debug_tests/Cargo.toml: no edition set: defaulting to the 2015 edition while the latest is 2021
   Compiling tinyvec_macros v0.1.1
   Compiling unicode-bidi v0.3.15
   Compiling percent-encoding v2.3.1 (/Users/brooks/github.com/servo/rust-url/percent_encoding)
   Compiling tinyvec v1.8.0
   Compiling form_urlencoded v1.2.1 (/Users/brooks/github.com/servo/rust-url/form_urlencoded)
   Compiling unicode-normalization v0.1.23
   Compiling idna v0.5.0 (/Users/brooks/github.com/servo/rust-url/idna)
   Compiling url v2.5.2 (/Users/brooks/github.com/servo/rust-url/url)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 1.51s

Because this feature is only enabled when the target OS is wasi and the target ENV is p2, this shouldn't affect any other functionality

[brooksmtownsend]

Hey @valenting just pinging for awareness 🙂

[codecov]

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[brooksmtownsend]

As far as I can tell the CI lints come in on Rust nightly and they aren't related to this change, same with the windows-latest run, but happy to address the lint issues here if desired

[brooksmtownsend]

@hsivonen would it be possible to get a review here? I'm not sure who the maintainers are, just looking for a set of eyes 😄

[Manishearth]

FWIW I think it is an extremely poor choice on rustc's side to make an API conditionally need a feature gate. But that appears to be deliberate choice on their behalf so there's not much I can do about this. I'm fine merging this, but not a fan.

I've filed an upstream bug: rust-lang/rust#130323