This commit improves the dependency injection mechanism by introducing a
custom `injectKey` function.
Key improvements are:
- Enforced type consistency during dependency registration and
instantiation.
- Simplified injection process, abstracting away the complexity with a
uniform API, regardless of the dependency's lifetime.
- Eliminated the possibility of `undefined` returns during dependency
injection, promoting fail-fast behavior.
- Removed the necessity for type casting to `symbol` for injection keys
in unit tests by using existing types.
- Consalidated imports, combining keys and injection functions in one
`import` statement.
