musig: Move MUSIG_CHAINCODE to musig.cpp

This is the only place where it is used.

src/musig.cpp

@@ -7,6 +7,13 @@
 
 #include <secp256k1_musig.h>
 
+//! MuSig2 chaincode as defined by BIP 328
+using namespace util::hex_literals;
+constexpr uint256 MUSIG_CHAINCODE{
+    // Use immediate lambda to work around GCC-14 bug https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117966
+    []() consteval { return uint256{"868087ca02a6f974c4598924c36b57762d32cb45717167e300622c7167e38965"_hex_u8}; }(),
+};
+
 static bool GetMuSig2KeyAggCache(const std::vector<CPubKey>& pubkeys, secp256k1_musig_keyagg_cache& keyagg_cache)
 {
     // Parse the pubkeys

src/musig.h

@@ -14,15 +14,6 @@ struct secp256k1_musig_keyagg_cache;
 class MuSig2SecNonceImpl;
 struct secp256k1_musig_secnonce;
 
-//! MuSig2 chaincode as defined by BIP 328
-using namespace util::hex_literals;
-constexpr uint256 MUSIG_CHAINCODE{
-    // Use immediate lambda to work around GCC-14 bug https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117966
-    []() consteval { return uint256{"868087ca02a6f974c4598924c36b57762d32cb45717167e300622c7167e38965"_hex_u8}; }(),
-};
-
-
-
 constexpr size_t MUSIG2_PUBNONCE_SIZE{66};
 
 //! Compute the full aggregate pubkey from the given participant pubkeys in their current order.