feat: add GetConfirmedHeight method to CoinJoin class

This commit introduces a new method, GetConfirmedHeight, to the CoinJoin class, allowing retrieval of the confirmed height. This addition enhances the functionality of the CoinJoin module, providing better access to transaction state information.

Author: PastaPastaPasta

src/coinjoin/coinjoin.h

@@ -287,6 +287,7 @@ class CCoinJoinBroadcastTx
     bool Sign(const CActiveMasternodeManager& mn_activeman);
     [[nodiscard]] bool CheckSignature(const CBLSPublicKey& blsPubKey) const;
 
+    [[nodiscard]] std::optional<int> GetConfirmedHeight() const { return nConfirmedHeight; }
     void SetConfirmedHeight(std::optional<int> nConfirmedHeightIn) { assert(nConfirmedHeightIn == std::nullopt || *nConfirmedHeightIn > 0); nConfirmedHeight = nConfirmedHeightIn; }
     bool IsExpired(const CBlockIndex* pindex, const llmq::CChainLocksHandler& clhandler) const;
     [[nodiscard]] bool IsValidStructure() const;