First pass at uniformed types, specs and docs

- spec public functions (skipping controllers, views, live views and
components)
- use types instead of explanations in docs
- remove redundant docs
- fix typos

lib/open_ai.ex

@@ -1,10 +1,19 @@
 defmodule OpenAI do
   alias OpenAI.API
 
+  @type chat_stream_opts :: [
+          model: String.t(),
+          temperature: float(),
+          instructions: String.t(),
+          on_chunk: (String.t() -> any())
+        ]
+
+  @spec gpt(OpenAI.Completion.t()) :: {:ok, map()} | {:error, term()}
   def gpt(completion) do
     API.gpt(completion, config())
   end
 
+  @spec chat_stream([map()], chat_stream_opts()) :: :ok | {:error, String.t()}
   def chat_stream(messages, opts \\ []) when is_list(messages) do
     model = Keyword.get(opts, :model, "gpt-4.1")
     temperature = Keyword.get(opts, :temperature, 0.7)
@@ -17,6 +26,7 @@ defmodule OpenAI do
     end
   end
 
+  @spec embeddings(String.t()) :: {:ok, [float()]} | {:error, term()}
   def embeddings(text) do
     API.get_embeddings(text, config())
   end