[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/log/caller.go

@@ -19,7 +19,8 @@ package log
 
 import (
 	"runtime"
-	"strings"
+
+	"codeberg.org/gruf/go-caller"
 )
 
 // Caller fetches the calling function name, skipping 'depth'.
@@ -27,29 +28,6 @@ import (
 //go:noinline
 func Caller(depth int) string {
 	pcs := make([]uintptr, 1)
-
-	// Fetch calling func using depth.
 	_ = runtime.Callers(depth, pcs)
-	fn := runtime.FuncForPC(pcs[0])
-
-	if fn == nil {
-		return ""
-	}
-
-	// Get func name.
-	name := fn.Name()
-
-	// Drop all but package and function name, no path.
-	if idx := strings.LastIndex(name, "/"); idx >= 0 {
-		name = name[idx+1:]
-	}
-
-	const params = `[...]`
-
-	// Drop any function generic type parameter markers.
-	if idx := strings.Index(name, params); idx >= 0 {
-		name = name[:idx] + name[idx+len(params):]
-	}
-
-	return name
+	return caller.Get(pcs[0])
 }