Rename the request mid-chunk flag to describe what it actually tracks (#25720)

test/registered/unit/managers/test_hisparse_unit.py

@@ -52,7 +52,7 @@ def _make_req(rid="test-req-0", origin_input_ids=None, output_ids=None):
         finished_reason=None,
         hisparse_staging=False,
         staging=False,
-        is_chunked=0,
+        inflight_middle_chunks=0,
     )
     req.finished = lambda: req.finished_reason is not None
     return req

test/registered/unit/managers/test_scheduler_chunked_req_gate.py

@@ -33,7 +33,7 @@ def _make_req(
     req.prefix_indices = prefix_indices
     req.req_pool_idx = req_pool_idx
     req.extend_input_len = extend_input_len
-    req.is_chunked = 0
+    req.inflight_middle_chunks = 0
     req.host_hit_length = 0
     req.cache_protected_len = 0
     req.skip_radix_cache_insert = False