Initial work on Vision support in text conversations and Image Editing

This is a huge patch which does some major refactoring like:

- renaming "Image Generation" to "Image Creation" in most places,
  to better match its new command (`!bai image create`)

- relocating image creation command (`!bai image` -> `!bai image create`),
  so it wouldn't conflict with the new image editing command (`!bai image edit`)

- introducing a new image editing command (`!bai image edit`), which
  is meant to work only with the OpenAI provider, but doesn't fully work yet
  due to https://github.com/64bit/async-openai/issues/364, though a next patch will fix it

- adding support for reading images off of Matrix conversations and forwarding them to
  text conversations. Works for OpenAI, but not for Anthropic yet
  (requires custom patches) and not for OpenAI-Compat (no support for
  images there)

- relocating some utils around (base64, mime)

src/agent/provider/controller.rs

@@ -1,10 +1,10 @@
 use crate::{agent::AgentPurpose, conversation::llm::Conversation};
 
 use super::{
-    ImageGenerationParams, SpeechToTextParams, SpeechToTextResult,
+    ImageGenerationParams, ImageEditParams, SpeechToTextParams, SpeechToTextResult,
     entity::{
-        ImageGenerationResult, PingResult, TextGenerationParams, TextGenerationResult,
-        TextToSpeechParams, TextToSpeechResult,
+        ImageGenerationResult, ImageEditResult, ImageSource, PingResult, TextGenerationParams,
+        TextGenerationResult, TextToSpeechParams, TextToSpeechResult,
     },
 };
 
@@ -42,6 +42,13 @@ pub trait ControllerTrait {
         params: ImageGenerationParams,
     ) -> impl std::future::Future<Output = anyhow::Result<ImageGenerationResult>> + Send;
 
+    fn create_image_edit(
+        &self,
+        prompt: &str,
+        images: Vec<ImageSource>,
+        params: ImageEditParams,
+    ) -> impl std::future::Future<Output = anyhow::Result<ImageEditResult>> + Send;
+
     fn text_to_speech(
         &self,
         text: &str,
@@ -166,6 +173,23 @@ impl ControllerTrait for ControllerType {
         }
     }
 
+    async fn create_image_edit(
+        &self,
+        prompt: &str,
+        images: Vec<ImageSource>,
+        params: ImageEditParams,
+    ) -> anyhow::Result<ImageEditResult> {
+        match &self {
+            ControllerType::OpenAI(controller) => controller.create_image_edit(prompt, images, params).await,
+            ControllerType::OpenAICompat(controller) => {
+                controller.create_image_edit(prompt, images, params).await
+            }
+            ControllerType::Anthropic(controller) => {
+                controller.create_image_edit(prompt, images, params).await
+            }
+        }
+    }
+
     async fn text_to_speech(
         &self,
         text: &str,