[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>

testrig/util.go

@@ -31,7 +31,7 @@ import (
 	"code.superseriousbusiness.org/gotosocial/internal/messages"
 	"code.superseriousbusiness.org/gotosocial/internal/processing/workers"
 	"code.superseriousbusiness.org/gotosocial/internal/state"
-	"codeberg.org/gruf/go-kv/v2"
+	"codeberg.org/gruf/go-kv/v2/format"
 )
 
 // Starts workers on the provided state using noop processing functions.
@@ -282,7 +282,6 @@ func WaitFor(condition func() bool) bool {
 
 // dump returns debug output of 'v'.
 func dump(v any) string {
-	var kv kv.Field
-	kv.V = v
-	return kv.Value(false)
+	buf := format.Global.Append(nil, v, format.DefaultArgs())
+	return string(buf)
 }