Add production features: slog adapter, scan helpers, slow query logging, pool stats, tracer passthrough, test tx isolation

- slog.go: SlogLogger adapts *slog.Logger to dbx.Logger interface
- scan.go: Collect[T] and CollectOne[T] generic helpers using pgx.RowToStructByName
- cluster.go: slow query logging via Config.SlowQueryThreshold (Warn level in queryEnd)
- stats.go: PoolStats with Cluster.Stats() aggregating pool stats across all nodes
- config.go/node.go: NodeConfig.Tracer passthrough for pgx.QueryTracer (OpenTelemetry)
- options.go: WithSlowQueryThreshold and WithTracer functional options
- dbxtest/tx.go: RunInTx runs callback in always-rolled-back transaction for test isolation

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

README.md

@@ -50,6 +50,9 @@ cluster.RunTx(ctx, func(ctx context.Context, tx pgx.Tx) error {
 | `healthChecker` | Background goroutine that pings all nodes on an interval. |
 | `Querier` injection | `InjectQuerier` / `ExtractQuerier` — context-based Querier for service layers. |
 | `MetricsHook` | Optional callbacks: query start/end, retry, node up/down, replica fallback. |
+| `SlogLogger` | Adapts `*slog.Logger` to the `dbx.Logger` interface. |
+| `Collect`/`CollectOne` | Generic scan helpers — read rows directly into structs via `pgx.RowToStructByName`. |
+| `PoolStats` | Aggregate pool statistics across all nodes via `cluster.Stats()`. |
 
 ## Routing
 
@@ -159,6 +162,60 @@ dbx.PgErrorCode(err)          // extract raw PG error code
 
 Sentinel errors: `ErrNoHealthyNode`, `ErrClusterClosed`, `ErrRetryExhausted`.
 
+## slog integration
+
+```go
+cluster, _ := dbx.NewCluster(ctx, dbx.Config{
+    Master: dbx.NodeConfig{DSN: "postgres://..."},
+    Logger: dbx.NewSlogLogger(slog.Default()),
+})
+```
+
+## Scan helpers
+
+Generic functions that eliminate row scanning boilerplate:
+
+```go
+type User struct {
+    ID   int    `db:"id"`
+    Name string `db:"name"`
+}
+
+users, err := dbx.Collect[User](ctx, cluster, "SELECT id, name FROM users WHERE active = $1", true)
+
+user, err := dbx.CollectOne[User](ctx, cluster, "SELECT id, name FROM users WHERE id = $1", 42)
+// returns pgx.ErrNoRows if not found
+```
+
+## Slow query logging
+
+```go
+cluster, _ := dbx.NewCluster(ctx, dbx.Config{
+    Master:             dbx.NodeConfig{DSN: "postgres://..."},
+    Logger:             dbx.NewSlogLogger(slog.Default()),
+    SlowQueryThreshold: 100 * time.Millisecond,
+})
+// queries exceeding threshold are logged at Warn level
+```
+
+## Pool stats
+
+```go
+stats := cluster.Stats()
+fmt.Println(stats.TotalConns, stats.IdleConns, stats.AcquireCount)
+// per-node stats: stats.Nodes["master"], stats.Nodes["replica-1"]
+```
+
+## OpenTelemetry / pgx tracer
+
+Pass any `pgx.QueryTracer` (e.g., `otelpgx.NewTracer()`) to instrument all queries:
+
+```go
+dbx.ApplyOptions(&cfg, dbx.WithTracer(otelpgx.NewTracer()))
+```
+
+Or set per-node via `NodeConfig.Tracer`.
+
 ## dbxtest helpers
 
 The `dbxtest` package provides test helpers:
@@ -171,6 +228,18 @@ func TestMyRepo(t *testing.T) {
 }
 ```
 
+### Transaction isolation for tests
+
+```go
+func TestCreateUser(t *testing.T) {
+    c := dbxtest.NewTestCluster(t)
+    dbxtest.RunInTx(t, c, func(ctx context.Context, q dbx.Querier) {
+        // all changes are rolled back after fn returns
+        _, _ = q.Exec(ctx, "INSERT INTO users (name) VALUES ($1)", "test")
+    })
+}
+```
+
 Set `DBX_TEST_DSN` env var to override the default DSN (`postgres://postgres:postgres@localhost:5432/dbx_test?sslmode=disable`).
 
 ## Requirements