refactor: call the benchmark's comparison the legacy format

The README, a comment in :Reflect and tests/Benchmark named the project
whose transaction log this library replaces. That name means nothing to
people using the library, so the benchmark's reference implementation is
now the `Legacy` namespace, its column reads `legacy ms`, and the prose
describes it as the hand-rolled iostream format Crafter.DB replaces.
Timings and logic are unchanged; the suite still passes.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

interfaces/Crafter.DB-Reflect.cppm

@@ -72,7 +72,7 @@ export namespace Crafter::DB {
         return raw.substr(dot + 1, end - dot - 1);
     }
 
-    // The type's qualified name as the compiler spells it ("Nostro::Transaction").
+    // The type's qualified name as the compiler spells it ("Ledger::Transaction").
     // Used in diagnostics only, so the exact spelling is not load-bearing.
     template<class T>
     consteval std::string_view TypeName() {