refactor: merge validation into MetricCallback, simplify progress bar to optimizer steps

- Remove separate ValidationCallback, merge into MetricCallback
- Progress bar now tracks optimizer steps instead of micro-steps
- Remove unused log_interval config field and CLI flag
- Fix validation all_reduce: use SUM(loss, count) instead of AVG
- Simplify metric logging: always log every optimizer step
- Add grad_norm display to progress bar

astrai/trainer/trainer.py

@@ -34,13 +34,12 @@ class Trainer:
                 cfg.ckpt_dir,
                 cfg.ckpt_interval,
             ),
-            CallbackFactory.create("validation"),
             CallbackFactory.create(
-                "metric_logger",
+                "metric",
                 log_dir=cfg.log_dir,
                 save_interval=cfg.ckpt_interval,
-                log_interval=cfg.log_interval,
                 metrics=cfg.metrics,
+                val_step=cfg.val_step,
             ),
             CallbackFactory.create("progress_bar", cfg.n_epoch),
             CallbackFactory.create("gradient_clipping", cfg.max_grad_norm),