apacheGH-34722: [C++][Parquet] Minor: Update wording of Parquet NextP…

…age (apache#35368)

### Rationale for this change

This change update wording of Parquet `NextPage`. It will reuse same decompression/decrypt buffer internal. So, use should attension it syntax.

### What changes are included in this PR?

No code change, just add some comments.

### Are these changes tested?

No need

### Are there any user-facing changes?

No.

* Closes: apache#34722

Lead-authored-by: mwish <maplewish117@gmail.com>
Co-authored-by: mwish <1506118561@qq.com>
Co-authored-by: Will Jones <willjones127@gmail.com>
Signed-off-by: Will Jones <willjones127@gmail.com>

cpp/src/arrow/buffer.h

@@ -63,7 +63,11 @@ class ARROW_EXPORT Buffer {
 
   Buffer(const uint8_t* data, int64_t size, std::shared_ptr<MemoryManager> mm,
          std::shared_ptr<Buffer> parent = NULLPTR)
-      : is_mutable_(false), data_(data), size_(size), capacity_(size), parent_(parent) {
+      : is_mutable_(false),
+        data_(data),
+        size_(size),
+        capacity_(size),
+        parent_(std::move(parent)) {
     SetMemoryManager(std::move(mm));
   }
 

cpp/src/parquet/column_reader.cc

@@ -275,6 +275,11 @@ class SerializedPageReader : public PageReader {
   }
 
   // Implement the PageReader interface
+  //
+  // The returned Page contains references that aren't guaranteed to live
+  // beyond the next call to NextPage(). SerializedPageReader reuses the
+  // decryption and decompression buffers internally, so if NextPage() is
+  // called then the content of previous page might be invalidated.
   std::shared_ptr<Page> NextPage() override;
 
   void set_max_page_header_size(uint32_t size) override { max_page_header_size_ = size; }

cpp/src/parquet/column_reader.h

@@ -152,6 +152,9 @@ class PARQUET_EXPORT PageReader {
 
   // @returns: shared_ptr<Page>(nullptr) on EOS, std::shared_ptr<Page>
   // containing new Page otherwise
+  //
+  // The returned Page may contain references that aren't guaranteed to live
+  // beyond the next call to NextPage().
   virtual std::shared_ptr<Page> NextPage() = 0;
 
   virtual void set_max_page_header_size(uint32_t size) = 0;