Add repository-wide TypeScript typecheck

[jeffwidman]

Summary

• make the root TypeScript project cover both source and test files
• use that project for ESLint and remove the redundant ESLint-only configuration
• add a typecheck script using tsc --noEmit
• run typechecking in the main test workflow after the fast formatting check

This matches the explicit typecheck used by dependabot/fetch-metadata. Neither ncc nor a future esbuild migration provides semantic TypeScript checking.

TypeScript configuration

The root tsconfig.json previously included only src/**/*.ts. Because ESLint uses type-aware rules and also lints files under __tests__/, tsconfig.eslint.json was added to extend the root configuration with both source and test files.

This PR makes the root configuration the canonical repository-wide TypeScript project by including both directories there. TypeScript, ESLint, editors, and CI can therefore use the same project, and the ESLint-specific configuration is no longer needed. Packaging remains scoped by the explicit ncc entry points, so including tests in the TypeScript project does not add them to the production bundles. The same remains true for a future esbuild migration.

Validation

• npm run format-check
• npm run typecheck
• npm run lint-check
• GITHUB_ACTOR=github-actions GITHUB_EVENT_NAME=pull_request npm test -- --runInBand
• npm run package

[Copilot]

Pull request overview

Adds explicit TypeScript project type-checking to CI, covering source and test files without emitting output.

Changes:

• Adds an npm run typecheck script.
• Runs type-checking in the main test workflow.

Show a summary per file

File	Description
package.json	Defines the TypeScript type-check command.
.github/workflows/test.yml	Executes type-checking during CI.

Review details

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• Review effort level: Balanced