fix: eslint & typescript the __tests__ directory

[andykenward]

Currently, the project doesn't lint or type check the __tests__ directory of files.

This pull request resolves this issue via

• ESLint "overrides" for the __tests__ directory that enables the eslint-plugin-jest
• Include __tests__ in the cli npm run lint
• Refactor the tsconfig.json to include the __tests__ directory.
• Add a tsconfig.build.json to extend tsconfig.json to exclude the __tests__ directory for usage via npm run build cli.