fixes the handler's minimum level throughout its lifetime.
Setting it to a [LevelVar] allows the level to be varied dynamically.
A LevelVar holds a Level and is safe to read or write from multiple
goroutines.
To vary the level dynamically for an entire program, first initialize
a global LevelVar:

	var programLevel = new(slog.LevelVar) // Info by default

Then use the LevelVar to construct a handler, and make it the default:

}

func TestHandlerEnabled(t *testing.T) {
	levelVar := func(l Level) *LevelVar {
		var al LevelVar
		al.Set(l)
		return &al
	}

	for _, test := range []struct {
		leveler Leveler
		want    bool
	}{
		{nil, true},
		{LevelWarn, false},
		{&LevelVar{}, true}, // defaults to Info
		{levelVar(LevelWarn), false},
		{LevelDebug, true},
		{levelVar(LevelDebug), true},
	} {

pkg log/slog, method (*Level) UnmarshalText([]uint8) error #56345
pkg log/slog, method (*LevelVar) Level() Level #56345
pkg log/slog, method (*LevelVar) MarshalText() ([]uint8, error) #56345
pkg log/slog, method (*LevelVar) Set(Level) #56345
pkg log/slog, method (*LevelVar) String() string #56345
pkg log/slog, method (*LevelVar) UnmarshalText([]uint8) error #56345

package slog

import (
	"context"
	"log"
	loginternal "log/internal"
	"log/slog/internal"
	"runtime"
	"sync/atomic"
	"time"
)

var defaultLogger atomic.Pointer[Logger]

var logLoggerLevel LevelVar

// SetLogLoggerLevel controls the level for the bridge to the [log] package.
//
// Before [SetDefault] is called, slog top-level logging functions call the default [log.Logger].

	// The handler discards records with lower levels.
	// If Level is nil, the handler assumes LevelInfo.
	// The handler calls Level.Level for each record processed;
	// to adjust the minimum level dynamically, use a LevelVar.
	Level Leveler

	// ReplaceAttr is called to rewrite each non-group attribute before it is logged.
	// The attribute's value has been resolved (see [Value.Resolve]).