fix: classify future-version ledgers with changed record shape correctly, not as corrupt

Version-check now runs on the parseLedger failure path too, so a v3 blob whose record shape actually changed reports FutureVersion instead of Unreadable, avoiding the corrupt-blob "clear it" advice. Also closes the six minor findings.

src/shell/actions/prune_action.cpp

@@ -50,7 +50,9 @@ void doBankPruneFolder(ReaSamplerSession& session) {
                    "ReaSampler than this one, so its records cannot be read safely. It "
                    "has been left intact and will NOT be overwritten. Reopen the project "
                    "with that newer version -- do NOT clear this key from here, that "
-                   "would discard tracking records this build cannot see.\n";
+                   "would discard tracking records this build cannot see. The block is "
+                   "held for the rest of this session, and until then no new capture is "
+                   "persisted to the ledger either.\n";
         }
         if (!report.unreadableUsageKeys.empty()) {
             msg += "One or more instance usage records could not be read or decoded. "