Pipeline training support + priority based rollout scheduler (#358)

* add

* add priority rolluot scheduler

* groupwise

* add

* add

* fix

* put it back

* add

* add postprocess

* resolve comments and fix bugs

* fix

Author: mayinghan

eval_protocol/pytest/buffer.py

@@ -0,0 +1,82 @@
+import asyncio
+import os
+from collections import defaultdict
+from typing import List, Dict
+
+from eval_protocol.models import EvaluationRow
+
+class MicroBatchDataBuffer:
+    """
+    Buffers evaluation results and writes them to disk in minibatches.
+    Waits for all runs of a sample to complete before considering it ready and flush to disk.
+    """
+    def __init__(self, num_runs: int, batch_size: int, output_path_template: str):
+        self.num_runs = num_runs
+        self.batch_size = batch_size
+        self.output_path_template = output_path_template
+        self.pending_samples: Dict[str, List[EvaluationRow]] = defaultdict(list)  # row_id -> list[EvaluationRow]
+        self.completed_samples_buffer: List[List[EvaluationRow]] = []  # List[List[EvaluationRow]]
+        self.batch_index = 0
+        self.lock = asyncio.Lock()
+
+    async def add_result(self, row: EvaluationRow):
+        """
+        Add a single evaluation result.
+        Thread-safe/Coroutine-safe.
+        """
+        async with self.lock:
+            row_id = row.input_metadata.row_id
+            if not row_id:
+                # Should not happen in valid EP workflow, unique row_id is required to group things together properly
+                return
+            
+            self.pending_samples[row_id].append(row)
+            
+            if len(self.pending_samples[row_id]) >= self.num_runs:
+                # Sample completed (all runs finished)
+                completed_rows = self.pending_samples.pop(row_id)
+                self.completed_samples_buffer.append(completed_rows)
+                
+                if len(self.completed_samples_buffer) >= self.batch_size:
+                    await self._flush_unsafe()
+
+    async def _flush_unsafe(self):
+        """
+        not thread safe, assumes lock is held by called
+        """
+        if not self.completed_samples_buffer:
+            return
+
+        if "{index}" in self.output_path_template:
+            output_path = self.output_path_template.format(index=self.batch_index)
+            mode = "w"
+        else:
+            output_path = self.output_path_template
+            mode = "a"  # Append if no index placeholder
+
+        # Ensure directory exists
+        os.makedirs(os.path.dirname(os.path.abspath(output_path)), exist_ok=True)
+        
+        # Write flattened rows
+        with open(output_path, mode) as f:
+            for sample_rows in self.completed_samples_buffer:
+                for row in sample_rows:
+                    f.write(row.model_dump_json() + "\n")
+        
+        self.completed_samples_buffer = []
+        self.batch_index += 1
+
+    async def close(self):
+        """
+        Flush any remaining samples in the buffer.
+        """
+        async with self.lock:
+            # Also flush pending (incomplete) samples to avoid data loss
+            if self.pending_samples:
+                for rows in self.pending_samples.values():
+                    self.completed_samples_buffer.append(rows)
+                self.pending_samples.clear()
+
+            if self.completed_samples_buffer:
+                await self._flush_unsafe()
+