feat(turbopack): wasm file write support and available_parallelism for worker pool

[xusd320]

Changes

turbo-tasks-fs

• Add wasm32-specific file write/remove path via wasm_fs_offload client, gated behind #[cfg(all(target_family = "wasm", target_os = "unknown"))]
• Fix symlink error message formatting

turbopack-node

• Extract available_parallelism into a dedicated module for cross-platform concurrency detection
• Simplify get_evaluate_pool to use available_parallelism() directly instead of available_parallelism().map_or(1, |v| v.get())
• Clean up import formatting in evaluate.rs

[gemini-code-assist]

Code Review

This pull request introduces WASM-specific file system operations in turbo-tasks-fs and refactors turbopack-node to use a local available_parallelism module. A review comment identifies an improvement opportunity in the WASM file handling logic, suggesting a refactor to eliminate redundant matching and the use of unreachable!() to improve code clarity and safety.

[gemini-code-assist]

The WASM-specific file operation block contains redundant logic and an unnecessary double-match pattern. By cloning the content Arc once before the match, you can bind the inner file value directly in the first match arm, avoiding the need for a second let...else with an unreachable!() check. This also ensures the content remains alive across the .await points in a cleaner way.

                #[cfg(all(target_family = "wasm", target_os = "unknown"))]
                {
                    let content = self.content.clone();
                    match &*content {
                        FileContent::Content(file) => {
                            let create_directory = compare == FileComparison::Create;
                            if create_directory && let Some(parent) = full_path.parent() {
                                self.inner.create_directory(parent).await.with_context(|| {
                                    format!(
                                        "failed to create directory {parent:?} for write to \
                                         {full_path:?}",
                                    )
                                })?;
                            }
                            wasm_fs_offload::CLIENT
                                .write(&full_path, file.content().to_bytes())
                                .instrument(tracing::info_span!("write file", name = ?full_path))
                                .await
                                .with_context(|| format!("failed to write to {full_path:?}"))?;
                        }
                        FileContent::NotFound => {
                            wasm_fs_offload::CLIENT
                                .remove_file(&full_path)
                                .instrument(tracing::info_span!("remove file", name = ?full_path))
                                .await
                                .with_context(|| format!("removing {full_path:?} failed"))?;
                        }
                    }
                }