How those formatted parts are concatenated.
A function that formats the log record. This function is called with the formatted values and should return a string. Note that the formatted should not include a newline character at the end.
By default, this is a function that formats the log record as follows:
2023-11-14 22:13:20.000 +00:00 [INF] category·subcategory: Hello, world!
(values: FormattedValues) => string