[Performance] Memoize isStdinPiped in cli-kit

[gonzaloriestra]

Why is this change needed?

The isStdinPiped function performs a synchronous fstatSync(0) call to determine if stdin is piped. In a CLI environment, this status remains constant throughout the process execution. Repeated calls to this function (either directly or via other utilities like readStdinString) result in redundant system calls.

How to test your changes?

CI

Post-deployment steps

None.

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PR created automatically by Jules for task 16902672566824217517 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>;
+/**
+ * Reset the memoized value for the stdin piped check.
+ * This is only used for testing.
+ */
+export declare function _resetIsStdinPipedCache(): void;
 /**
  * Check if stdin has piped data available.
  * This distinguishes between actual piped input (e.g., )