Dependency Injection Container

Implement a simple DI container:

const container = new Container();
container.register('name', factoryExpr, deps?)
container.resolve('name')  // instantiate with resolved deps

• register(name, factoryExpr, deps) — register a factory **expression

string** (e.g. '() => 42' or '(x) => x * 2') with optional dependency
names. Convert it to a function via new Function('return ' + expr)().

• resolve(name) — resolve the service, auto-resolving its dependencies

recursively. Throw on circular deps or missing registrations.

solve(registrations, target) replays registrations then resolves a service.

Each registration is a tuple [name, factoryExpr, deps?].