FIX: removal corruption caused by stale _lastBucket pointing into freed buckets.

Correct chain unlinking so tail removal no longer leaves dangling Next links.
Ensure moved entry slot updates the owning bucket after compaction.
Introduce kickout-on-insert to restore home-bucket invariant for foreign heads.
Prevents overlapping chains and hard-to-reproduce lookup failures.

Author: Wsm2110

src/Concurrent/CMap.cs

@@ -12,7 +12,7 @@
 
 #nullable enable
 
-namespace Faster.Map;
+namespace Faster.Map.Core;
 
 /// <summary>
 /// A specialized implementation of <see cref="RobinhoodMap{TKey, TValue, THasher}"/> that