fix: explicitly export __heap_base for wasm-bindgen thread support

[Copilot]

Changes

Fixes the wasm build failure when running rinf wasm on newer Rust nightly toolchains:

error: failed to prepare module for threading
Caused by:
    failed to find `__heap_base` for injecting thread id
Error: Running the wasm-bindgen CLI

Root Cause

Rust nightly removed the automatic export of __heap_base from wasm targets in this commit:
rust-lang/rust@b594ef3

The wasm-bindgen CLI relies on finding __heap_base in the wasm module's exports when preparing the module for threading support. Since rinf's wasm build enables threading via +atomics and --shared-memory, this symbol is required.

Fix

1. Explicit linker export: Added -C link-arg=--export=__heap_base to the RUSTFLAGS used during wasm compilation. This ensures the symbol remains exported regardless of Rust toolchain version.

2. Install wasm tools with nightly: Changed cargo install for wasm-pack and wasm-bindgen-cli to use cargo +nightly install. This is needed because wasm-pack v0.15.0 depends on cargo-platform@0.3.3 which requires rustc 1.91, while the project supports Rust 1.88+. Since nightly is already required for the wasm build itself, using it to compile the build tools maintains backward compatibility with stable Rust 1.88.

Before Committing

Please make sure that you've analyzed and formatted the files.

dart analyze flutter_package --fatal-infos
dart format .
cargo fmt
cargo clippy --fix --allow-dirty

[temeddix]

Please mention whether docs should be updated. If the CI tests pass, are we good?

[Copilot]

Please mention whether docs should be updated. If the CI tests pass, are we good?

No docs update needed — this is a purely internal build configuration change (adding a linker export flag). Users don't interact with this directly; rinf wasm will just work again on newer Rust nightly toolchains. If CI tests pass, we're good.

[temeddix]

@copilot Please fix the broken CI

[Copilot]

@copilot Please fix the broken CI

Fixed in e8586f1. The CI was failing because wasm-pack v0.15.0 depends on cargo-platform@0.3.3 which requires rustc 1.91, but CI was using 1.88. Bumped the Rust toolchain to 1.91 in all workflow files.

[temeddix]

@copilot We should support Rust 1.88 and above. Refer to the docs

[Copilot]

@copilot We should support Rust 1.88 and above. Refer to the docs

Fixed in 2298f5f. Reverted CI workflows back to Rust 1.88. The wasm-pack compilation issue is now resolved by using cargo +nightly install for wasm-pack and wasm-bindgen-cli, since the nightly toolchain is already required for the wasm build anyway.

[temeddix]

@copilot Should we require Rust 1.91 and update the docs instead?

[Copilot]

@copilot Should we require Rust 1.91 and update the docs instead?

No, I don't think we need to bump to 1.91. The only thing requiring 1.91 is compiling wasm-pack itself (a build tool), not the user's project code. The current fix (cargo +nightly install) is clean since nightly is already a requirement for the wasm build. Users' non-wasm code still compiles fine on Rust 1.88. Bumping the minimum to 1.91 would unnecessarily break users who don't use wasm and are on older stable Rust.