feat: added token counter command to CLI

[cpacker]

 % letta run                                                

? Would you like to select an existing agent? No

🧬 Creating new agent...
? Select LLM model: gpt-4 [type=openai] [ip=https://api.openai.com/v1]
? Select LLM context window limit (hit enter for default): 4001
? Select embedding model: letta-free [type=hugging-face] [ip=https://embeddings.memgpt.ai]
->  🤖 Using persona profile: 'sam_pov'
->  🧑 Using human profile: 'basic'
->  🛠️  7 tools: send_message, conversation_search, conversation_search_date, archival_memory_insert, archival_memory_search, core_memory_append, core_memory_replace
🎉 Created new agent 'QuickApple' (id=agent-ac297c2b-f9e7-4882-9acb-3f7d6d8be3c2)

Hit enter to begin (will request first Letta message)


💭 Chad's first login. I should welcome him to set a friendly tone. It's crucial not only to make him comfortable but also to engage him on a deeper level, reflecting my persona's characteristics.
🤖 Hello Chad, welcome! It's a pleasure to meet you. I'm Sam. Do share, what's one thing you're curious about today?

> Enter your message: /tokens

2510 / 4001