[optimization] Avoid unnecessary locking in single and scoped instances

[JustinBis]

ScopedInstanceFactory and SingleInstanceFactory both lock on every call to get. This adds unnecessary overhead since locking is only required during the first initialization of an object.

Koin should add double-checked locking so that we can avoid locking every time we inject a single or scoped instance.

See Dagger's DoubleCheck for an example in Java that is widely employed: https://github.com/google/dagger/blob/f8a09b29683687720ae3e0e5ac241f3a4a054d6e/java/dagger/internal/DoubleCheck.java#L29

Example implementation

    // In SingleInstanceFactory
    @Volatile
    private var value: T? = null

    override fun get(context: InstanceContext): T {
        // Fast path to avoid locking if this instance is already initialized
        if (!isCreated(context)) {
            KoinPlatformTools.synchronized(this) {
                if (!isCreated(context)) {
                    value = create(context)
                }
            }
        }
        return getValue()
    }

Note that the multiplatform @Volatile is necessary for this to be correct on JVM and native platforms.