chore: move .mocharc.js to root and delete library copies

[GautamSharda]

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For googleapis/librarian#4583

[gemini-code-assist]

Code Review

This pull request centralizes Mocha configuration by removing local .mocharc files across the monorepo and updating the root configuration. Feedback highlights that switching to ESM exports in the root .mocharc.js could cause runtime errors in CommonJS environments. Furthermore, the reviewer pointed out that the omission of the recursive flag in the centralized config might lead to silent test skips, as several deleted local configurations previously relied on it for test discovery.

[gemini-code-assist]

Changing the export to export default in a .js file will cause a SyntaxError at runtime if the root package.json does not contain "type": "module". Since this configuration is being centralized to replace local versions that were using CommonJS (module.exports), it is safer to maintain CommonJS compatibility to ensure it works across all packages in the monorepo.

Additionally, please ensure that the config object (defined in the lines above) includes "recursive": true. Several of the deleted local configurations (e.g., in gapic-node-processing, grafeas, and google-cloud-monitoring) specifically enabled this flag. If it is missing from this centralized root configuration, Mocha will fail to discover tests in subdirectories for those packages, leading to silent test skips in CI.

Suggested change

	export default config
	module.exports = config