[Performance] Memoize isWsl result

[gonzaloriestra]

WHY are these changes introduced?

The isWsl function in packages/cli-kit/src/public/node/system.ts performs a dynamic import of the is-wsl package every time it is called. Since the environment (WSL or not) does not change during the execution of the process, this result can be safely memoized to avoid redundant imports and computations.

WHAT is this pull request doing?

This PR memoizes the promise returned by the dynamic is-wsl import in the isWsl function.

• Introduced a module-level memoizedIsWsl variable.
• Updated isWsl to use the nullish coalescing assignment operator (??=) to cache and return the promise.
• Exported an internal _resetIsWsl function to allow clearing the cache during unit tests, ensuring test isolation.
• Added unit tests in packages/cli-kit/src/public/node/system.test.ts to verify memoization and reset behavior.

How to test your changes?

CI

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• The change is user-facing — I've identified the correct bump type (patch for bug fixes · minor for new features · major for breaking changes) and added a changeset with pnpm changeset add

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PR created automatically by Jules for task 1458224654387623489 started by @gonzaloriestra

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[github-actions]

Differences in type declarations

We detected differences in the type declarations generated by Typescript for this branch compared to the baseline ('main' branch). Please, review them to ensure they are backward-compatible. Here are some important things to keep in mind:

• Some seemingly private modules might be re-exported through public modules.
• If the branch is behind main you might see odd diffs, rebase main into this branch.

New type declarations

We found no new type declarations in this PR

Existing type declarations

packages/cli-kit/dist/public/node/system.d.ts

@@ -111,6 +111,11 @@ export declare function isCI(): boolean;
  * @returns True if the current environment is a WSL environment.
  */
 export declare function isWsl(): Promise<boolean>;
+/**
+ * Resets the memoized value for the WSL check.
+ * This is used for testing purposes.
+ */
+export declare function _resetIsWsl(): void;
 /**
  * Check if stdin has piped data available.
  * This distinguishes between actual piped input (e.g., )