[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/level.go

@@ -17,22 +17,18 @@
 
 package log
 
-// LEVEL defines a level of logging.
-type LEVEL uint8
-
-// Default levels of logging.
-const (
-	UNSET LEVEL = 0
-	PANIC LEVEL = 1
-	ERROR LEVEL = 100
-	WARN  LEVEL = 150
-	INFO  LEVEL = 200
-	DEBUG LEVEL = 250
-	TRACE LEVEL = 254
-	ALL   LEVEL = ^LEVEL(0)
+import (
+	"code.superseriousbusiness.org/gotosocial/internal/log/level"
 )
 
-// CanLog returns whether an incoming log of 'lvl' can be logged against receiving level.
-func (loglvl LEVEL) CanLog(lvl LEVEL) bool {
-	return loglvl > lvl
-}
+type LEVEL = level.LEVEL
+
+const (
+	PANIC = level.PANIC
+	ERROR = level.ERROR
+	WARN  = level.WARN
+	INFO  = level.INFO
+	DEBUG = level.DEBUG
+	TRACE = level.TRACE
+	UNSET = level.UNSET
+)