(pubk)key: mark Derive() as nodiscard

src/key.h

@@ -146,7 +146,7 @@ public:
     bool SignSchnorr(const uint256& hash, Span<unsigned char> sig, const uint256* merkle_root, const uint256& aux) const;
 
     //! Derive BIP32 child key.
-    bool Derive(CKey& keyChild, ChainCode &ccChild, unsigned int nChild, const ChainCode& cc) const;
+    [[nodiscard]] bool Derive(CKey& keyChild, ChainCode &ccChild, unsigned int nChild, const ChainCode& cc) const;
 
     /**
      * Verify thoroughly whether a private key and a public key match.
@@ -176,7 +176,7 @@ struct CExtKey {
 
     void Encode(unsigned char code[BIP32_EXTKEY_SIZE]) const;
     void Decode(const unsigned char code[BIP32_EXTKEY_SIZE]);
-    bool Derive(CExtKey& out, unsigned int nChild) const;
+    [[nodiscard]] bool Derive(CExtKey& out, unsigned int nChild) const;
     CExtPubKey Neuter() const;
     void SetSeed(Span<const std::byte> seed);
 };

src/pubkey.h

@@ -218,7 +218,7 @@ public:
     bool Decompress();
 
     //! Derive BIP32 child pubkey.
-    bool Derive(CPubKey& pubkeyChild, ChainCode &ccChild, unsigned int nChild, const ChainCode& cc) const;
+    [[nodiscard]] bool Derive(CPubKey& pubkeyChild, ChainCode &ccChild, unsigned int nChild, const ChainCode& cc) const;
 };
 
 class XOnlyPubKey
@@ -327,7 +327,7 @@ struct CExtPubKey {
     void Decode(const unsigned char code[BIP32_EXTKEY_SIZE]);
     void EncodeWithVersion(unsigned char code[BIP32_EXTKEY_WITH_VERSION_SIZE]) const;
     void DecodeWithVersion(const unsigned char code[BIP32_EXTKEY_WITH_VERSION_SIZE]);
-    bool Derive(CExtPubKey& out, unsigned int nChild) const;
+    [[nodiscard]] bool Derive(CExtPubKey& out, unsigned int nChild) const;
 };
 
 /** Users of this module must hold an ECCVerifyHandle. The constructor and