Make XOnlyPubKey act like byte container

src/pubkey.h

@@ -222,6 +222,12 @@ private:
     uint256 m_keydata;
 
 public:
+    /** Construct an empty x-only pubkey. */
+    XOnlyPubKey() = default;
+
+    XOnlyPubKey(const XOnlyPubKey&) = default;
+    XOnlyPubKey& operator=(const XOnlyPubKey&) = default;
+
     /** Construct an x-only pubkey from exactly 32 bytes. */
     explicit XOnlyPubKey(Span<const unsigned char> bytes);
 
@@ -234,7 +240,14 @@ public:
 
     const unsigned char& operator[](int pos) const { return *(m_keydata.begin() + pos); }
     const unsigned char* data() const { return m_keydata.begin(); }
-    size_t size() const { return m_keydata.size(); }
+    static constexpr size_t size() { return decltype(m_keydata)::size(); }
+    const unsigned char* begin() const { return m_keydata.begin(); }
+    const unsigned char* end() const { return m_keydata.end(); }
+    unsigned char* begin() { return m_keydata.begin(); }
+    unsigned char* end() { return m_keydata.end(); }
+    bool operator==(const XOnlyPubKey& other) const { return m_keydata == other.m_keydata; }
+    bool operator!=(const XOnlyPubKey& other) const { return m_keydata != other.m_keydata; }
+    bool operator<(const XOnlyPubKey& other) const { return m_keydata < other.m_keydata; }
 };
 
 struct CExtPubKey {

src/uint256.h

@@ -75,7 +75,7 @@ public:
         return &m_data[WIDTH];
     }
 
-    unsigned int size() const
+    static constexpr unsigned int size()
     {
         return sizeof(m_data);
     }