[Performance] Memoize hasGit check in cli-kit

[gonzaloriestra]

WHY are these changes introduced?

The hasGit function in cli-kit executes git --version every time it's called. Spawning a child process is relatively expensive. In commands that perform multiple environment checks or analytics collection, this redundant execution can measurably slow down the CLI.

WHAT is this pull request doing?

Memoizes the result of hasGit() using a module-level promise. This ensures that git --version is executed at most once during the CLI's execution. Subsequent calls will return the cached result.
Includes an exported _resetHasGit() utility to maintain test isolation.

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 and added a changeset with pnpm changeset add

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PR created automatically by Jules for task 9108386419192763021 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/context/local.d.ts

@@ -132,6 +132,11 @@ export declare function cloudEnvironment(env?: NodeJS.ProcessEnv): {
  * @returns A promise that resolves with the value.
  */
 export declare function hasGit(): Promise<boolean>;
+/**
+ * Resets the memoized hasGit value.
+ * This is useful for testing.
+ */
+export declare function _resetHasGit(): void;
 /**
  * Gets info on the CI platform the CLI is running on, if applicable.
  *