[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/ap/extract.go

@@ -97,11 +97,12 @@ func ExtractActivityData(activity pub.Activity, rawJSON map[string]any) ([]TypeO
 func ExtractAccountables(arr []TypeOrIRI) ([]Accountable, []TypeOrIRI) {
 	var accounts []Accountable
 
-	for i := 0; i < len(arr); i++ {
+	for i := 0; i < len(arr); {
 		elem := arr[i]
 
 		if elem.IsIRI() {
 			// skip IRIs
+			i++ // iter
 			continue
 		}
 
@@ -112,6 +113,7 @@ func ExtractAccountables(arr []TypeOrIRI) ([]Accountable, []TypeOrIRI) {
 		// Try cast AS type as Accountable.
 		account, ok := ToAccountable(t)
 		if !ok {
+			i++ // iter
 			continue
 		}
 
@@ -130,11 +132,12 @@ func ExtractAccountables(arr []TypeOrIRI) ([]Accountable, []TypeOrIRI) {
 func ExtractStatusables(arr []TypeOrIRI) ([]Statusable, []TypeOrIRI) {
 	var statuses []Statusable
 
-	for i := 0; i < len(arr); i++ {
+	for i := 0; i < len(arr); {
 		elem := arr[i]
 
 		if elem.IsIRI() {
 			// skip IRIs
+			i++ // iter
 			continue
 		}
 
@@ -145,10 +148,11 @@ func ExtractStatusables(arr []TypeOrIRI) ([]Statusable, []TypeOrIRI) {
 		// Try cast AS type as Statusable.
 		status, ok := ToStatusable(t)
 		if !ok {
+			i++ // iter
 			continue
 		}
 
-		// Add casted Statusable type.
+		// Append casted Statusable type.
 		statuses = append(statuses, status)
 
 		// Drop elem from slice.
@@ -163,11 +167,12 @@ func ExtractStatusables(arr []TypeOrIRI) ([]Statusable, []TypeOrIRI) {
 func ExtractPollOptionables(arr []TypeOrIRI) ([]PollOptionable, []TypeOrIRI) {
 	var options []PollOptionable
 
-	for i := 0; i < len(arr); i++ {
+	for i := 0; i < len(arr); {
 		elem := arr[i]
 
 		if elem.IsIRI() {
 			// skip IRIs
+			i++ // iter
 			continue
 		}
 
@@ -178,6 +183,7 @@ func ExtractPollOptionables(arr []TypeOrIRI) ([]PollOptionable, []TypeOrIRI) {
 		// Try cast as PollOptionable.
 		option, ok := ToPollOptionable(t)
 		if !ok {
+			i++ // iter
 			continue
 		}