Fix RCU test by not reusing BC from disposed store

Author: PaulusParssinen

libs/storage/Tsavorite/cs/src/core/Allocator/BlittableAllocatorImpl.cs

@@ -156,6 +156,8 @@ public long GetPhysicalAddress(long logicalAddress)
 
             // Index of page within the circular buffer
             var pageIndex = (int)((logicalAddress >> LogPageSizeBits) & (BufferSize - 1));
+
+            Debug.Assert(IsAllocated(pageIndex));
             return (long)(pointers[pageIndex] + offset);
         }
 

libs/storage/Tsavorite/cs/src/core/Allocator/SpanByteAllocatorImpl.cs

@@ -236,6 +236,8 @@ public long GetPhysicalAddress(long logicalAddress)
 
             // Index of page within the circular buffer
             var pageIndex = (int)((logicalAddress >> LogPageSizeBits) & (BufferSize - 1));
+
+            Debug.Assert(IsAllocated(pageIndex));
             return (long)(pointers[pageIndex] + offset);
         }
 

libs/storage/Tsavorite/cs/test/MiscTests.cs

@@ -198,6 +198,7 @@ public void ForceRCUAndRecover([Values(UpdateOp.Upsert, UpdateOp.Delete)] Update
 
                 _ = store.Recover(token);
                 session = store.NewSession<InputStruct, OutputStruct, Empty, FunctionsCopyOnWrite>(copyOnWrite);
+                bContext = session.BasicContext;
 
                 using (var iterator = store.Log.Scan(store.Log.BeginAddress, store.Log.TailAddress))
                 {