[Performance] Memoize isWsl

[gonzaloriestra]

This PR optimizes the isWsl utility function by memoizing its result. Since the WSL status of an environment does not change during the lifetime of the process, we can safely cache the promise from the dynamic import and return it for all subsequent calls.

Performance Impact:

• Reduces overhead of repeated dynamic imports.
• Returns the same promise instance, allowing for reference equality checks if needed.
• Improves performance in analytics and metadata reporting paths.

Testing:

• Added new unit tests in packages/cli-kit/src/public/node/system.test.ts.
• Verified that isWsl correctly identifies the environment (mocked).
• Verified that multiple calls return the exact same promise instance.
• Ran full test suite for @shopify/cli-kit.

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PR created automatically by Jules for task 2044910693505345155 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 +111,10 @@ 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.
+ */
+export declare function _resetIsWsl(): void;
 /**
  * Check if stdin has piped data available.
  * This distinguishes between actual piped input (e.g., )