Add wasm64-unknown-unknown target support

[audreyt]

Summary

Extend wasm-pack to support wasm64-unknown-unknown targets alongside existing wasm32 support, enabling wasm-pack build and wasm-pack test to work with WebAssembly memory64 modules.

Closes #1464.

Motivation

The WebAssembly memory64 proposal has reached standardization phase, and Rust nightly ships a wasm64-unknown-unknown target. The underlying toolchain now has wasm-bindgen#5004 implements for memory64 codegen support, and downstream getrandom has a corresponding PR at getrandom#819. wasm-pack is the last piece: its build and test pipelines hardcode wasm32-unknown-unknown as the target triple, so wasm-pack build --target wasm64-unknown-unknown silently ignores the user's intent.

Changes

5 files changed (+49 −29) — all mechanical plumbing to thread the target triple through instead of hardcoding it:

• src/build/mod.rs — Parameterize cargo_build_wasm() and cargo_build_wasm_tests() to accept a target_triple argument instead of hardcoding wasm32-unknown-unknown via CARGO_BUILD_TARGET
• src/command/build.rs — Pass self.target_triple through to cargo_build_wasm(); add --enable-memory64 to wasm-opt args when the target starts with wasm64
• src/command/test.rs — Extract --target from extra_options (defaulting to wasm32-unknown-unknown); construct CARGO_TARGET_<TRIPLE>_RUNNER env var dynamically instead of hardcoding CARGO_TARGET_WASM32_UNKNOWN_UNKNOWN_RUNNER; thread target_triple through to all test steps (node, Chrome, Firefox, Safari) and webdriver_env()
• src/test/mod.rs — Parameterize cargo_test_wasm() to accept target_triple and pass it to cargo test --target
• src/manifest/mod.rs — Generalize the cdylib error message from "wasm32-unknown-unknown" to "WebAssembly"

Usage

# Build
wasm-pack build --target web -- --target wasm64-unknown-unknown

# Test
wasm-pack test --node -- --target wasm64-unknown-unknown

The -- --target wasm64-unknown-unknown is passed through as a Cargo extra option. When omitted, behavior is unchanged (wasm32-unknown-unknown).

Testing

• Verified wasm-pack build with wasm32 targets is unchanged (no regressions)
• Validated end-to-end with a real-world project (web-rwkv) compiled to wasm64-unknown-unknown — a 1.7B parameter LLM inference engine that requires >4 GB memory