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

core/state/snapshot/generate_test.go

@@ -601,7 +601,7 @@ func testGenerateWithExtraAccounts(t *testing.T, scheme string) {
 }
 
 func enableLogging() {
-	log.Root().SetHandler(log.LvlFilterHandler(log.LvlTrace, log.StreamHandler(os.Stderr, log.TerminalFormat(true))))
+	log.SetDefault(log.NewLogger(log.NewTerminalHandlerWithLevel(os.Stderr, log.LevelTrace, true)))
 }
 
 // Tests that snapshot generation when an extra account with storage exists in the snap state.

core/txpool/blobpool/blobpool_test.go

@@ -319,7 +319,7 @@ func verifyPoolInternals(t *testing.T, pool *BlobPool) {
 //   - 3. All transactions after a nonce gap must be dropped
 //   - 4. All transactions after an underpriced one (including it) must be dropped
 func TestOpenDrops(t *testing.T) {
-	log.Root().SetHandler(log.LvlFilterHandler(log.LvlTrace, log.StreamHandler(os.Stderr, log.TerminalFormat(true))))
+	log.SetDefault(log.NewLogger(log.NewTerminalHandlerWithLevel(os.Stderr, log.LevelTrace, true)))
 
 	// Create a temporary folder for the persistent backend
 	storage, _ := os.MkdirTemp("", "blobpool-")
@@ -600,7 +600,7 @@ func TestOpenDrops(t *testing.T) {
 //   - 2. Eviction thresholds are calculated correctly for the sequences
 //   - 3. Balance usage of an account is totals across all transactions
 func TestOpenIndex(t *testing.T) {
-	log.Root().SetHandler(log.LvlFilterHandler(log.LvlTrace, log.StreamHandler(os.Stderr, log.TerminalFormat(true))))
+	log.SetDefault(log.NewLogger(log.NewTerminalHandlerWithLevel(os.Stderr, log.LevelTrace, true)))
 
 	// Create a temporary folder for the persistent backend
 	storage, _ := os.MkdirTemp("", "blobpool-")
@@ -689,7 +689,7 @@ func TestOpenIndex(t *testing.T) {
 // Tests that after indexing all the loaded transactions from disk, a price heap
 // is correctly constructed based on the head basefee and blobfee.
 func TestOpenHeap(t *testing.T) {
-	log.Root().SetHandler(log.LvlFilterHandler(log.LvlTrace, log.StreamHandler(os.Stderr, log.TerminalFormat(true))))
+	log.SetDefault(log.NewLogger(log.NewTerminalHandlerWithLevel(os.Stderr, log.LevelTrace, true)))
 
 	// Create a temporary folder for the persistent backend
 	storage, _ := os.MkdirTemp("", "blobpool-")
@@ -776,7 +776,7 @@ func TestOpenHeap(t *testing.T) {
 // Tests that after the pool's previous state is loaded back, any transactions
 // over the new storage cap will get dropped.
 func TestOpenCap(t *testing.T) {
-	log.Root().SetHandler(log.LvlFilterHandler(log.LvlTrace, log.StreamHandler(os.Stderr, log.TerminalFormat(true))))
+	log.SetDefault(log.NewLogger(log.NewTerminalHandlerWithLevel(os.Stderr, log.LevelTrace, true)))
 
 	// Create a temporary folder for the persistent backend
 	storage, _ := os.MkdirTemp("", "blobpool-")
@@ -868,7 +868,7 @@ func TestOpenCap(t *testing.T) {
 // specific to the blob pool. It does not do an exhaustive transaction validity
 // check.
 func TestAdd(t *testing.T) {
-	log.Root().SetHandler(log.LvlFilterHandler(log.LvlTrace, log.StreamHandler(os.Stderr, log.TerminalFormat(true))))
+	log.SetDefault(log.NewLogger(log.NewTerminalHandlerWithLevel(os.Stderr, log.LevelTrace, true)))
 
 	// seed is a helper tumpe to seed an initial state db and pool
 	type seed struct {