refactor: migrates to typescript

[cacieprins]

• Migrates @cypress/code-coverage to typescript, building with tsc for both cjs and esm projects
• Removes dead code relating to Cypress <v10
• Resolves CI issues with windows tests
• Makes use of type hints for coverage data & placeholder object manipulation
• Adds a test app for esm integration host projects

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Note

Medium Risk
Touches the published module entrypoints and build/CI pipeline, so release-time packaging and runtime compatibility (Cypress plugin hooks, coverage merging) are the main risks despite largely type-focused refactors.

Overview
Migrates the package implementation from JS/CommonJS sources to a TypeScript build output. Core entrypoints (task, plugins, support, use-babelrc, and middleware) are rewritten/typed in TS and package.json now exports from dist/ via a new tsc build (tsconfig.json, build/prepublishOnly, updated prettier globs).

CI is reworked to build once and reuse dist across jobs (new build-dist, renamed/reshaped matrix verify-test-apps, Windows job now builds + installs test app deps). Adds a new test-apps/esm-example and documents it in the README.

Coverage utilities and tests are updated for the TS migration (typed NYC/coverage objects, js-yaml load API, simplified support-file filtering, vitest coverage include paths, and TS test rewrites), plus dependency updates for TypeScript and type packages.

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