feat(spanner): migrate batch 1 core samples and tests

[angelcaamal]

Description

Fixes Internal: b/497969229

Note: Before submitting a pull request, please open an issue for discussion if you are not associated with Google.

Checklist

• I have followed guidelines from CONTRIBUTING.MD and Samples Style Guide
• Tests pass: npm test (see Testing)
• Lint pass: npm run lint (see Style)
• Required CI tests pass (see CI testing)
• These samples need a new API enabled in testing projects to pass (let us know which ones)
• These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• This pull request is from a branch created directly off of GoogleCloudPlatform/nodejs-docs-samples. Not a fork.
• This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• This sample adds a new sample directory, and I created GitHub Actions workflow for this sample
• This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• Please merge this PR for me once it is approved

Note: Any check with (dev), (experimental), or (legacy) can be ignored and should not block your PR from merging (see CI testing).

[gemini-code-assist]

Code Review

This pull request introduces a comprehensive suite of Node.js samples for Google Cloud Spanner, covering CRUD operations, database and index management, encryption, and commit statistics, alongside a robust system test suite. The review feedback highlights several critical improvements: addressing a concurrency bug in the test cleanup logic, ensuring database closures are properly awaited for session pool management, and using string representations for INT64 values to prevent precision issues. Additionally, the feedback recommends avoiding unnecessary mutations of global library objects and removing redundant keywords to enhance code quality and maintainability.

[snippet-bot]

Here is the summary of changes.

You are about to add 16 region tags.

• spanner/crud.js:21, tag spanner_update_data
• spanner/crud.js:62, tag spanner_insert_data
• spanner/crud.js:116, tag spanner_delete_data
• spanner/crud.js:188, tag spanner_query_data
• spanner/crud.js:232, tag spanner_read_data
• spanner/crud.js:281, tag spanner_read_stale_data
• spanner/database-create-with-encryption-key.js:23, tag spanner_create_database_with_encryption_key
• spanner/database-create-with-version-retention-period.js:23, tag spanner_create_database_with_version_retention_period
• spanner/database-update.js:26, tag spanner_update_database
• spanner/get-commit-stats.js:18, tag spanner_get_commit_stats
• spanner/index-create-storing.js:26, tag spanner_create_storing_index
• spanner/index-create.js:26, tag spanner_create_index
• spanner/index-query-data.js:28, tag spanner_query_data_with_index
• spanner/schema.js:20, tag spanner_create_database
• spanner/schema.js:78, tag spanner_add_column
• spanner/schema.js:124, tag spanner_query_data_with_new_column

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