fix(dependency-injection): include requiredBy chain in UnsatisfiedDependencyException message

[deer]

Previously, UnsatisfiedDependencyException only named the unsatisfied dependency itself. When a failure was buried several levels deep in the injection graph, there was no way to tell which top-level component triggered the resolution.

The requiredBy chain was already threaded through AbstractResolvable but never included in the exception message. This change walks the chain at throw time and appends it:

Unable to resolve com.example.DatabaseConnection:
  required by TaskExecutor
  required by DefaultProgram
  required by Engine