logger: bug with shared fields slice

[alkur-gh]

https://github.com/unistack-org/micro/blob/bff40bd3179b3af4bc1decb76a45aaadf3c61b5b/logger/options.go#L32

Because of the shared slice with capacity of 6, multiple cloned loggers write fields to the same place.

Snippet:

package main

import (
	"context"
	"fmt"

	zerolog "go.unistack.org/micro-logger-zerolog/v3"
	"go.unistack.org/micro/v3/logger"
)

func main() {
	logger.DefaultLogger = zerolog.NewLogger(
		zerolog.ReportCaller(),
		logger.WithLevel(logger.InfoLevel),
		logger.WithCallerSkipCount(5),
		//logger.WithFields(),
	)

	if err := logger.DefaultLogger.Init(); err != nil {
		panic(err)
	}

	ctx := context.Background()

	fields := func() any {
		return logger.DefaultLogger.Clone().Options().Fields
	}

	log := logger.DefaultLogger.Clone().Fields("my", "name", "is", "jojo")
	log2 := logger.DefaultLogger.Clone().Fields("who", "are")

	fmt.Printf("fields: %v (%p)\n", fields(), fields())
	fmt.Printf("log fields: %v (%p)\n", log.Options().Fields, log.Options().Fields)
	fmt.Printf("log2 fields: %v (%p)\n", log2.Options().Fields, log2.Options().Fields)

	logger.DefaultLogger.Clone().Fields("hello", "world").Trace(ctx)

	fmt.Printf("fields: %v (%p)\n", fields(), fields())
	fmt.Printf("log fields: %v (%p)\n", log.Options().Fields, log.Options().Fields)
	fmt.Printf("log2 fields: %v (%p)\n", log2.Options().Fields, log2.Options().Fields)
}

module demo

go 1.20

require (
	go.unistack.org/micro-logger-zerolog/v3 v3.8.4
	go.unistack.org/micro/v3 v3.10.39
)

require (
	github.com/mattn/go-colorable v0.1.12 // indirect
	github.com/mattn/go-isatty v0.0.14 // indirect
	github.com/pkg/errors v0.9.1 // indirect
	github.com/rs/zerolog v1.29.0 // indirect
	golang.org/x/sys v0.7.0 // indirect
)

Actual result:

fields: [] (0xc0000b4300)
log fields: [who are is jojo] (0xc0000b4300)
log2 fields: [who are] (0xc0000b4300)
fields: [] (0xc0000b4300)
log fields: [hello world is jojo] (0xc0000b4300)
log2 fields: [hello world] (0xc0000b4300)

Expected:

fields: [] (0x0)
log fields: [my name is jojo] (0xc0000d0040)
log2 fields: [who are] (0xc0000ce0c0)
fields: [] (0x0)
log fields: [my name is jojo] (0xc0000d0040)
log2 fields: [who are] (0xc0000ce0c0)