fix(test): replace C++17 structured bindings with C++14 compatible code

Problem:
- Two test cases in test_buffer.cpp used structured bindings (auto [a, b])
- Structured bindings are a C++17 feature
- Project requires C++14 compatibility

Solution:
- Replace 'auto [ptr, size] = buf.to_tuple()' with C++14 compatible code
- Use std::get<N>() to extract tuple elements
- Modified tests: ToTupleNonConst, ToTupleConst

Changes:
- Line 239: Use std::get<0/1>(tuple) instead of structured binding
- Line 252: Use std::get<0/1>(tuple) instead of structured binding
- Add explanatory comments for clarity

This ensures the test suite compiles with C++14 standard.

Author: mutouyun

test/test_buffer.cpp

@@ -236,7 +236,10 @@ TEST_F(BufferTest, ToTupleNonConst) {
 
   buffer buf(data, 25, DestructorTracker::destructor);
 
-  auto [ptr, size] = buf.to_tuple();
+  // C++14 compatible: use std::get instead of structured binding
+  auto tuple = buf.to_tuple();
+  auto ptr = std::get<0>(tuple);
+  auto size = std::get<1>(tuple);
   EXPECT_EQ(ptr, buf.data());
   EXPECT_EQ(size, buf.size());
   EXPECT_EQ(size, 25u);
@@ -249,7 +252,10 @@ TEST_F(BufferTest, ToTupleConst) {
 
   const buffer buf(data, 30, DestructorTracker::destructor);
 
-  auto [ptr, size] = buf.to_tuple();
+  // C++14 compatible: use std::get instead of structured binding
+  auto tuple = buf.to_tuple();
+  auto ptr = std::get<0>(tuple);
+  auto size = std::get<1>(tuple);
   EXPECT_EQ(ptr, buf.data());
   EXPECT_EQ(size, buf.size());
   EXPECT_EQ(size, 30u);