[feature + performance] add JSON logging format (#4355)

# Description

Adds JSON logging as an optional alternative log output format. In the process this moves our log formatting itself into a separate subpkg to make it more easily modular, and improves caller name getting with some calling function name caching.

## 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.
- [x] I/we have commented the added code, particularly in hard-to-understand areas.
- [x] I/we have made any necessary changes to documentation.
- [ ] I/we have added tests that cover new code.
- [x] 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/4355
Co-authored-by: kim <grufwub@gmail.com>
Co-committed-by: kim <grufwub@gmail.com>

internal/federation/federatingdb/util.go

@@ -20,6 +20,7 @@ package federatingdb
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 	"net/url"
 
 	"code.superseriousbusiness.org/activity/streams"
@@ -212,15 +213,23 @@ func getActivityContext(ctx context.Context) activityContext {
 // lazy-serialization along with error output.
 type serialize struct{ item vocab.Type }
 
+func (s serialize) MarshalJSON() ([]byte, error) {
+	m, err := ap.Serialize(s.item)
+	if err != nil {
+		return nil, fmt.Errorf("error serializing: %w", err)
+	}
+	return json.Marshal(m)
+}
+
 func (s serialize) String() string {
 	m, err := ap.Serialize(s.item)
 	if err != nil {
-		return "!(error serializing item: " + err.Error() + ")"
+		return "!(error serializing: " + err.Error() + ")"
 	}
 
 	b, err := json.Marshal(m)
 	if err != nil {
-		return "!(error json marshaling item: " + err.Error() + ")"
+		return "!(error marshaling: " + err.Error() + ")"
 	}
 
 	return byteutil.B2S(b)