Feature: LLava executor

KernelMemory update with adding the use of already loaded model

When using KernelMemory one may have already loaded a model which can then be used with this extension instead of loading the model again.

[LLama.KernelMemory] Fixed System.ArgumentException: EmbeddingMode must be true & #617

Add an Example and modifications to the interactive executor to enable Llava Models.

Just a preview / demo

This reverts commit 5fda26c610.

Chat session state management

* Previously when a conversation was forked this would result in both the parent and the child sharing exactly the same logits. Since sampling is allowed to modify logits this could lead to issues in sampling (e.g. one conversation is sampled and overwrites logits to be all zero, second conversation is sampled and generates nonsense). Fixed this by setting a "forked" flag, logits are copied if this flag is set. Flag is cleared next time the conversation is prompted so this extra copying only happens once after a fork occurs.

* Removed finalizer from `BatchedExecutor`. This class does not directly own any unmanaged resources so it is not necessary.

Replaced `BatchedExecutor.Prompt(string)` method with `BatchedExecutor.Create()` method. This improves the API in two ways:
 - A conversation can be created, without immediately prompting it
 - Other prompting overloads (e.g. prompt with token list) can be used without duplicating all the overloads onto `BatchedExecutor`

Added `BatchSize` property to `LLamaContext`