[performance] handle emoji refreshes asynchronously when fetched as part of account|status dereferences (#4486)

# Description

Updates our dereferencer emoji handling to work asynchronously when going through the route of account or status dereferencing.

closes https://codeberg.org/superseriousbusiness/gotosocial/issues/4485

## Checklist

- [x] I/we have read the [GoToSocial contribution guidelines](https://codeberg.org/superseriousbusiness/gotosocial/src/branch/main/CONTRIBUTING.md).
- [x] I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
- [x] I/we have not leveraged AI to create the proposed changes.
- [x] I/we have performed a self-review of added code.
- [x] I/we have written code that is legible and maintainable by others.
- [ ] I/we have commented the added code, particularly in hard-to-understand areas.
- [ ] I/we have made any necessary changes to documentation.
- [ ] I/we have added tests that cover new code.
- [ ] I/we have run tests and they pass locally with the changes.
- [x] I/we have run `go fmt ./...` and `golangci-lint run`.

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4486
Co-authored-by: kim <grufwub@gmail.com>
Co-committed-by: kim <grufwub@gmail.com>

internal/media/processingemoji.go

@@ -44,11 +44,6 @@ type ProcessingEmoji struct {
 	mgr       *Manager          // mgr instance (access to db / storage)
 }
 
-// ID returns the ID of the underlying emoji.
-func (p *ProcessingEmoji) ID() string {
-	return p.emoji.ID // immutable, safe outside mutex.
-}
-
 // LoadEmoji blocks until the static and fullsize image has been processed, and then returns the completed emoji.
 func (p *ProcessingEmoji) Load(ctx context.Context) (*gtsmodel.Emoji, error) {
 	emoji, done, err := p.load(ctx)
@@ -63,6 +58,33 @@ func (p *ProcessingEmoji) Load(ctx context.Context) (*gtsmodel.Emoji, error) {
 	return emoji, err
 }
 
+func (p *ProcessingEmoji) LoadAsync(deferred func()) *gtsmodel.Emoji {
+	p.mgr.state.Workers.Dereference.Queue.Push(func(ctx context.Context) {
+		if deferred != nil {
+			defer deferred()
+		}
+
+		if _, _, err := p.load(ctx); err != nil {
+			log.Errorf(ctx, "error loading emoji: %v", err)
+		}
+	})
+
+	// Placeholder returns a copy of internally stored processing placeholder,
+	// returning only the fields that may be known *before* completion,
+	// and as such all fields which are safe to concurrently read.
+	placeholder := new(gtsmodel.Emoji)
+	placeholder.ID = p.emoji.ID
+	placeholder.Shortcode = p.emoji.Shortcode
+	placeholder.Domain = p.emoji.Domain
+	placeholder.Cached = new(bool)
+	placeholder.ImageRemoteURL = p.emoji.ImageRemoteURL
+	placeholder.ImageStaticRemoteURL = p.emoji.ImageStaticRemoteURL
+	placeholder.Disabled = p.emoji.Disabled
+	placeholder.VisibleInPicker = p.emoji.VisibleInPicker
+	placeholder.CategoryID = p.emoji.CategoryID
+	return placeholder
+}
+
 // load is the package private form of load() that is wrapped to catch context canceled.
 func (p *ProcessingEmoji) load(ctx context.Context) (
 	emoji *gtsmodel.Emoji,