chore(pubsub): factor out the pub/sub pieces to use the test-utils library

[feywind]

After adding the test-utils library, this PR factors it out of the Pub/Sub library so that it's properly shared.

This currently contains the commits of #9229 - once that's merged, this one will get updated.

b/554057686

[gemini-code-assist]

Code Review

This pull request extracts and centralizes testing utilities into a new core/test-utils package, updating the handwritten/pubsub package to use it and removing duplicate local files. Feedback on the changes suggests simplifying the shortUUID implementation with slice to avoid unnecessary array allocations, resolving a missing .jsdoc.js configuration file referenced in the docs script, and using recursive wildcards in tsconfig.json to ensure nested files are compiled.

[gemini-code-assist]

The shortUUID function can be simplified and made more efficient by using slice instead of splitting the UUID string into an array and shifting it. This avoids unnecessary array allocation and the non-null assertion operator.

Suggested change

	function shortUUID(): string {
	return crypto.randomUUID().split('-').shift()!;
	}
	function shortUUID(): string {
	return crypto.randomUUID().slice(0, 8);
	}

[gemini-code-assist]

The docs script references .jsdoc.js, but this configuration file is not present in the core/test-utils directory. Running npm run docs will fail. Please add the missing .jsdoc.js file or update the script to use compodoc (since .compodocrc is present).

[gemini-code-assist]

Using flat wildcards like src/*.ts and test/*.ts only includes files directly in those directories. To ensure any nested files or subdirectories created in the future are also compiled and tested, use recursive wildcards.

Suggested change

	"src/*.ts",
	"test/*.ts"
	"src/**/*.ts",
	"test/**/*.ts"