fix(test): Fix buffer overflow in data_set caused by array placement new

ROOT CAUSE:
Array placement new (::new(buffer) T[N]) adds a hidden cookie (array size)
before the array elements in some compiler implementations (particularly MSVC).
The cookie is used for proper array destruction. However, the data_set buffer
was sized only for sizeof(T[N]), not accounting for the cookie overhead.

ISSUE:
- Buffer allocated: sizeof(rand_buf[LoopCount])
- Actual space needed: sizeof(cookie) + sizeof(rand_buf[LoopCount])
- Result: Cookie and part of array written beyond buffer boundary
- Consequence: Memory corruption, leading to invalid pointers in buffer objects

SYMPTOM:
In IPC.1v1 test, memcpy(buf, data, size) crashed because 'data' pointer
(from buffer::data()) pointed to corrupted/invalid memory address.

SOLUTION:
Replace array placement new with individual element placement new:
- Cast buffer to array pointer directly (no cookie needed)
- Construct each element individually with placement new
- Manually destroy each element in destructor

This approach:
- Eliminates cookie overhead
- Provides precise control over object lifetime
- Works consistently across all compilers

Fixes crash in IPC.1v1 test case on MSVC.

Author: mutouyun

test/test_ipc.cpp

@@ -84,22 +84,34 @@ void test_basic(char const * name) {
     EXPECT_EQ(que2.recv(), test2);
 }
 
-class data_set {
-    alignas(rand_buf) char datas_[sizeof(rand_buf[LoopCount])];
-    rand_buf *d_;
-
-public:
-    data_set() {
-        d_ = ::new(datas_) rand_buf[LoopCount];
-        for (int i = 0; i < LoopCount; ++i) {
-            d_[i].set_id(i);
-        }
-    }
-
-    rand_buf const *get() const noexcept {
-        return d_;
-    }
-} const data_set__;
+class data_set {
+    alignas(rand_buf) char datas_[sizeof(rand_buf[LoopCount])];
+    rand_buf *d_;
+
+public:
+    data_set() {
+        // Use individual placement new instead of array placement new
+        // Array placement new adds a cookie (array size) before the array,
+        // which would overflow the buffer. MSVC's implementation stores this
+        // cookie, causing buffer overflow and subsequent memory corruption.
+        d_ = reinterpret_cast<rand_buf *>(datas_);
+        for (int i = 0; i < LoopCount; ++i) {
+            ::new(d_ + i) rand_buf;
+            d_[i].set_id(i);
+        }
+    }
+
+    ~data_set() {
+        // Manually destroy each element since we used individual placement new
+        for (int i = 0; i < LoopCount; ++i) {
+            d_[i].~rand_buf();
+        }
+    }
+
+    rand_buf const *get() const noexcept {
+        return d_;
+    }
+} const data_set__;
 
 template <relat Rp, relat Rc, trans Ts, typename Que = chan<Rp, Rc, Ts>>
 void test_sr(char const * name, int s_cnt, int r_cnt) {