all: replace log15 with slog (#28187)

This PR replaces Geth's logger package (a fork of [log15](https://github.com/inconshreveable/log15)) with an implementation using slog, a logging library included as part of the Go standard library as of Go1.21.

Main changes are as follows:
* removes any log handlers that were unused in the Geth codebase.
* Json, logfmt, and terminal formatters are now slog handlers.
* Verbosity level constants are changed to match slog constant values.  Internal translation is done to make this opaque to the user and backwards compatible with existing `--verbosity` and `--vmodule` options.
* `--log.backtraceat` and `--log.debug` are removed.

The external-facing API is largely the same as the existing Geth logger.  Logger method signatures remain unchanged.

A small semantic difference is that a `Handler` can only be set once per `Logger` and not changed dynamically.  This just means that a new logger must be instantiated every time the handler of the root logger is changed.

----
For users of the `go-ethereum/log` module. If you were using this module for your own project, you will need to change the initialization. If you previously did 
```golang
log.Root().SetHandler(log.LvlFilterHandler(log.LvlInfo, log.StreamHandler(os.Stderr, log.TerminalFormat(true))))
```
You now instead need to do 
```golang
log.SetDefault(log.NewLogger(log.NewTerminalHandlerWithLevel(os.Stderr, log.LevelInfo, true)))
```
See more about reasoning here: https://github.com/ethereum/go-ethereum/issues/28558#issuecomment-1820606613

cmd/evm/internal/t8ntool/block.go

@@ -33,6 +33,7 @@ import (
 	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/rlp"
 	"github.com/urfave/cli/v2"
+	"golang.org/x/exp/slog"
 )
 
 //go:generate go run github.com/fjl/gencodec -type header -field-override headerMarshaling -out gen_header.go
@@ -216,9 +217,9 @@ func (i *bbInput) sealClique(block *types.Block) (*types.Block, error) {
 // BuildBlock constructs a block from the given inputs.
 func BuildBlock(ctx *cli.Context) error {
 	// Configure the go-ethereum logger
-	glogger := log.NewGlogHandler(log.StreamHandler(os.Stderr, log.TerminalFormat(false)))
-	glogger.Verbosity(log.Lvl(ctx.Int(VerbosityFlag.Name)))
-	log.Root().SetHandler(glogger)
+	glogger := log.NewGlogHandler(log.NewTerminalHandler(os.Stderr, false))
+	glogger.Verbosity(slog.Level(ctx.Int(VerbosityFlag.Name)))
+	log.SetDefault(log.NewLogger(glogger))
 
 	baseDir, err := createBasedir(ctx)
 	if err != nil {

cmd/evm/internal/t8ntool/transaction.go

@@ -33,6 +33,7 @@ import (
 	"github.com/ethereum/go-ethereum/rlp"
 	"github.com/ethereum/go-ethereum/tests"
 	"github.com/urfave/cli/v2"
+	"golang.org/x/exp/slog"
 )
 
 type result struct {
@@ -66,9 +67,9 @@ func (r *result) MarshalJSON() ([]byte, error) {
 
 func Transaction(ctx *cli.Context) error {
 	// Configure the go-ethereum logger
-	glogger := log.NewGlogHandler(log.StreamHandler(os.Stderr, log.TerminalFormat(false)))
-	glogger.Verbosity(log.Lvl(ctx.Int(VerbosityFlag.Name)))
-	log.Root().SetHandler(glogger)
+	glogger := log.NewGlogHandler(log.NewTerminalHandler(os.Stderr, false))
+	glogger.Verbosity(slog.Level(ctx.Int(VerbosityFlag.Name)))
+	log.SetDefault(log.NewLogger(glogger))
 
 	var (
 		err error

cmd/evm/internal/t8ntool/transition.go

@@ -24,6 +24,8 @@ import (
 	"os"
 	"path"
 
+	"golang.org/x/exp/slog"
+
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/common/hexutil"
 	"github.com/ethereum/go-ethereum/consensus/misc/eip1559"
@@ -81,9 +83,9 @@ type input struct {
 
 func Transition(ctx *cli.Context) error {
 	// Configure the go-ethereum logger
-	glogger := log.NewGlogHandler(log.StreamHandler(os.Stderr, log.TerminalFormat(false)))
-	glogger.Verbosity(log.Lvl(ctx.Int(VerbosityFlag.Name)))
-	log.Root().SetHandler(glogger)
+	glogger := log.NewGlogHandler(log.NewTerminalHandler(os.Stderr, false))
+	glogger.Verbosity(slog.Level(ctx.Int(VerbosityFlag.Name)))
+	log.SetDefault(log.NewLogger(glogger))
 
 	var (
 		err    error