refactor: Make XOnlyPubKey tolerate constexpr std::arrays

Length was already asserted inside of base_blob-ctor.

Author: hodlinator

src/pubkey.cpp

@@ -193,12 +193,6 @@ int ecdsa_signature_parse_der_lax(secp256k1_ecdsa_signature* sig, const unsigned
 static const std::vector<unsigned char> NUMS_H_DATA{ParseHex("50929b74c1a04954b78b4b6035e97a5e078a5a0f28ec96d547bfee9ace803ac0")};
 const XOnlyPubKey XOnlyPubKey::NUMS_H{NUMS_H_DATA};
 
-XOnlyPubKey::XOnlyPubKey(Span<const unsigned char> bytes)
-{
-    assert(bytes.size() == 32);
-    std::copy(bytes.begin(), bytes.end(), m_keydata.begin());
-}
-
 std::vector<CKeyID> XOnlyPubKey::GetKeyIDs() const
 {
     std::vector<CKeyID> out;

src/pubkey.h

@@ -254,7 +254,7 @@ class XOnlyPubKey
     bool IsNull() const { return m_keydata.IsNull(); }
 
     /** Construct an x-only pubkey from exactly 32 bytes. */
-    explicit XOnlyPubKey(Span<const unsigned char> bytes);
+    constexpr explicit XOnlyPubKey(std::span<const unsigned char> bytes) : m_keydata{bytes} {}
 
     /** Construct an x-only pubkey from a normal pubkey. */
     explicit XOnlyPubKey(const CPubKey& pubkey) : XOnlyPubKey(Span{pubkey}.subspan(1, 32)) {}