coins: add Reset on CCoinsViewCache

Add a Reset() method to CCoinsViewCache that clears cacheCoins,
cachedCoinsUsage, and hashBlock without flushing to the base view.

Co-authored-by: l0rinc <pap.lorinc@gmail.com>
Co-authored-by: sedited <seb.kung@gmail.com>

src/coins.cpp

@@ -274,6 +274,13 @@ void CCoinsViewCache::Sync()
     }
 }
 
+void CCoinsViewCache::Reset() noexcept
+{
+    cacheCoins.clear();
+    cachedCoinsUsage = 0;
+    hashBlock.SetNull();
+}
+
 void CCoinsViewCache::Uncache(const COutPoint& hash)
 {
     CCoinsMap::iterator it = cacheCoins.find(hash);

src/coins.h

@@ -376,6 +376,12 @@ protected:
     /* Cached dynamic memory usage for the inner Coin objects. */
     mutable size_t cachedCoinsUsage{0};
 
+    /**
+     * Discard all modifications made to this cache without flushing to the base view.
+     * This can be used to efficiently reuse a cache instance across multiple operations.
+     */
+    void Reset() noexcept;
+
 public:
     CCoinsViewCache(CCoinsView *baseIn, bool deterministic = false);