refactor: Return std::span from MakeByteSpan

In theory this commit should only touch the span.h header, because
std::span can implicilty convert into Span in most places, if needed.

However, at least when using the clang compiler, there are some
false-positive lifetimebound warnings and some implicit conversions can
not be resolved.

Thus, this refactoring commit also changed the affected places to
replace Span with std::span.

src/bip324.cpp

@@ -22,8 +22,8 @@
 #include <iterator>
 #include <string>
 
-BIP324Cipher::BIP324Cipher(const CKey& key, Span<const std::byte> ent32) noexcept :
+BIP324Cipher::BIP324Cipher(const CKey& key, std::span<const std::byte> ent32) noexcept
-    m_key(key)
+    : m_key(key)
 {
     m_our_pubkey = m_key.EllSwiftCreate(ent32);
 }

src/bip324.h

@@ -45,7 +45,7 @@ public:
     BIP324Cipher() = delete;
 
     /** Initialize a BIP324 cipher with specified key and encoding entropy (testing only). */
-    BIP324Cipher(const CKey& key, Span<const std::byte> ent32) noexcept;
+    BIP324Cipher(const CKey& key, std::span<const std::byte> ent32) noexcept;
 
     /** Initialize a BIP324 cipher with specified key (testing only). */
     BIP324Cipher(const CKey& key, const EllSwiftPubKey& pubkey) noexcept;

src/dbwrapper.cpp

@@ -402,12 +402,12 @@ void CDBIterator::SeekImpl(Span<const std::byte> key)
     m_impl_iter->iter->Seek(slKey);
 }
 
-Span<const std::byte> CDBIterator::GetKeyImpl() const
+std::span<const std::byte> CDBIterator::GetKeyImpl() const
 {
     return MakeByteSpan(m_impl_iter->iter->key());
 }
 
-Span<const std::byte> CDBIterator::GetValueImpl() const
+std::span<const std::byte> CDBIterator::GetValueImpl() const
 {
     return MakeByteSpan(m_impl_iter->iter->value());
 }

src/dbwrapper.h

@@ -130,8 +130,8 @@ private:
     const std::unique_ptr<IteratorImpl> m_impl_iter;
 
     void SeekImpl(Span<const std::byte> key);
-    Span<const std::byte> GetKeyImpl() const;
+    std::span<const std::byte> GetKeyImpl() const;
-    Span<const std::byte> GetValueImpl() const;
+    std::span<const std::byte> GetValueImpl() const;
 
 public:
 

src/pubkey.cpp

@@ -353,7 +353,7 @@ bool CPubKey::Derive(CPubKey& pubkeyChild, ChainCode &ccChild, unsigned int nChi
     return true;
 }
 
-EllSwiftPubKey::EllSwiftPubKey(Span<const std::byte> ellswift) noexcept
+EllSwiftPubKey::EllSwiftPubKey(std::span<const std::byte> ellswift) noexcept
 {
     assert(ellswift.size() == SIZE);
     std::copy(ellswift.begin(), ellswift.end(), m_pubkey.begin());

src/pubkey.h

@@ -317,7 +317,7 @@ public:
     EllSwiftPubKey() noexcept = default;
 
     /** Construct a new ellswift public key from a given serialization. */
-    EllSwiftPubKey(Span<const std::byte> ellswift) noexcept;
+    EllSwiftPubKey(std::span<const std::byte> ellswift) noexcept;
 
     /** Decode to normal compressed CPubKey (for debugging purposes). */
     CPubKey Decode() const;

src/span.h

@@ -266,14 +266,14 @@ Span<std::byte> AsWritableBytes(Span<T> s) noexcept
 }
 
 template <typename V>
-Span<const std::byte> MakeByteSpan(V&& v) noexcept
+auto MakeByteSpan(const V& v) noexcept
 {
-    return AsBytes(Span{std::forward<V>(v)});
+    return std::as_bytes(std::span{v});
 }
 template <typename V>
-Span<std::byte> MakeWritableByteSpan(V&& v) noexcept
+auto MakeWritableByteSpan(V&& v) noexcept
 {
-    return AsWritableBytes(Span{std::forward<V>(v)});
+    return std::as_writable_bytes(std::span{std::forward<V>(v)});
 }
 
 // Helper functions to safely cast basic byte pointers to unsigned char pointers.

src/test/util_tests.cpp

@@ -243,7 +243,7 @@ BOOST_AUTO_TEST_CASE(util_HexStr)
         constexpr std::string_view out_exp{"04678afdb0"};
         constexpr std::span in_s{HEX_PARSE_OUTPUT, out_exp.size() / 2};
         const Span<const uint8_t> in_u{MakeUCharSpan(in_s)};
-        const Span<const std::byte> in_b{MakeByteSpan(in_s)};
+        const std::span<const std::byte> in_b{MakeByteSpan(in_s)};
 
         BOOST_CHECK_EQUAL(HexStr(in_u), out_exp);
         BOOST_CHECK_EQUAL(HexStr(in_s), out_exp);