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/controller/utils/mime.rs

@@ -1,17 +0,0 @@
-use mxlink::mime;
-
-pub fn get_file_extension(mime_type: &mime::Mime) -> String {
-    match (mime_type.type_(), mime_type.subtype()) {
-        (mime::AUDIO, mime::BASIC) => "au",
-        (mime::AUDIO, mime::MPEG) => "mp3",
-        (mime::AUDIO, mime::MP4) => "m4a",
-        (mime::AUDIO, mime::OGG) => "ogg",
-        (mime::IMAGE, mime::BMP) => "bmp",
-        (mime::IMAGE, mime::GIF) => "gif",
-        (mime::IMAGE, mime::JPEG) => "jpg",
-        (mime::IMAGE, mime::PNG) => "png",
-        (mime::IMAGE, mime::SVG) => "svg",
-        _ => "bin",
-    }
-    .to_string()
-}

src/controller/utils/mod.rs

@@ -6,7 +6,6 @@ use crate::{
 };
 
 pub mod agent;
-pub(super) mod mime;
 pub mod text_to_speech;
 
 pub async fn get_text_body_or_complain<'a>(

src/controller/utils/text_to_speech.rs

@@ -3,7 +3,7 @@ use mxlink::{MatrixLink, MessageResponseType};
 
 use tracing::Instrument;
 
-use crate::controller::utils::mime::get_file_extension;
+use crate::utils::mime::get_file_extension;
 use crate::{
     Bot,
     agent::{AgentInstance, AgentPurpose, ControllerTrait, provider::TextToSpeechParams},