perf: Remove unnecessary caches (#5439)

This change removes the cache in `DatabaseNodeImp` and simplifies the caching logic in `SHAMapStoreImp`. As NuDB and RocksDB internally already use caches, additional caches in the code are not very valuable or may even be unnecessary, as also confirmed during preliminary performance analyses.

src/test/app/SHAMapStore_test.cpp

@@ -490,19 +490,8 @@ public:
         Env env(*this, envconfig(onlineDelete));
 
         /////////////////////////////////////////////////////////////
-        // Create the backend. Normally, SHAMapStoreImp handles all these
-        // details
-        auto nscfg = env.app().config().section(ConfigSection::nodeDatabase());
-
-        // Provide default values:
-        if (!nscfg.exists("cache_size"))
-            nscfg.set(
-                "cache_size", std::to_string(env.app().config().getValueFor(SizedItem::treeCacheSize, std::nullopt)));
-
-        if (!nscfg.exists("cache_age"))
-            nscfg.set(
-                "cache_age", std::to_string(env.app().config().getValueFor(SizedItem::treeCacheAge, std::nullopt)));
-
+        // Create NodeStore with two backends to allow online deletion of data.
+        // Normally, SHAMapStoreImp handles all these details.
         NodeStoreScheduler scheduler(env.app().getJobQueue());
 
         std::string const writableDb = "write";
@@ -510,9 +499,8 @@ public:
         auto writableBackend = makeBackendRotating(env, scheduler, writableDb);
         auto archiveBackend = makeBackendRotating(env, scheduler, archiveDb);
 
-        // Create NodeStore with two backends to allow online deletion of
-        // data
         constexpr int readThreads = 4;
+        auto nscfg = env.app().config().section(ConfigSection::nodeDatabase());
         auto dbr = std::make_unique<NodeStore::DatabaseRotatingImp>(
             scheduler,
             readThreads,