fix: remove fiber guard from non atomic section (#3381)

We might preempt when we serialize a big value and the code in journal was protected by an atomic guard triggering a check failed.

* remove fiber guard from non atomic section
* move LocalBlockingCounter to common

---------

Signed-off-by: kostas <kostas@dragonflydb.io>

src/server/common.h

@@ -15,6 +15,7 @@
 #include <string_view>
 #include <vector>
 
+#include "base/logging.h"
 #include "facade/facade_types.h"
 #include "facade/op_status.h"
 #include "util/fibers/fibers.h"
@@ -381,4 +382,28 @@ class ConditionGuard {
   ConditionFlag* enclosing_;
 };
 
+class LocalBlockingCounter {
+ public:
+  void lock() {
+    ++mutating_;
+  }
+
+  void unlock() {
+    DCHECK(mutating_ > 0);
+    --mutating_;
+    if (mutating_ == 0) {
+      cond_var_.notify_one();
+    }
+  }
+
+  void Wait() {
+    util::fb2::NoOpLock noop_lk_;
+    cond_var_.wait(noop_lk_, [this]() { return mutating_ == 0; });
+  }
+
+ private:
+  util::fb2::CondVarAny cond_var_;
+  size_t mutating_ = 0;
+};
+
 }  // namespace dfly