fix(dependency-injection): fix concurrency races in bindSet and auto-singleton registration

[deer]

• bindSet had a TOCTOU race between containsKey and computeIfAbsent on the ConcurrentHashMap of multibinding entries. Replaced with a single atomic compute call using an AtomicBoolean to track whether the entry was newly created, ensuring contributeBinding is called exactly once regardless of thread interleaving.
• Concurrent first-touch creation of an unbound @Singleton type could cause the losing thread to receive an unexpected BindingAlreadyExistsException from addBinding. The auto-registration path in getValue now catches BindingAlreadyExistsException and silently defers to the binding registered by the winning thread.