Flat map all the things

In an earlier commit, entity-manager gained required dependency
on std::flat_map.  This means that EM can only compile with gcc-15,
which the project only recently moved to.  Rather than move backwards,
port forward all uses of boost flat_map and flat_set to their std
equivalents.

Tested: entity-manager launches and enumerates devices on
gb200-obmc.

Change-Id: Id24803057711c60d5b00f436db80b27edbb756a3
Signed-off-by: Ed Tanous <etanous@nvidia.com>
diff --git a/src/entity_manager/entity_manager.cpp b/src/entity_manager/entity_manager.cpp
index a3b4a72..6bf3c52 100644
--- a/src/entity_manager/entity_manager.cpp
+++ b/src/entity_manager/entity_manager.cpp
@@ -16,7 +16,6 @@
 #include <boost/asio/io_context.hpp>
 #include <boost/asio/post.hpp>
 #include <boost/asio/steady_timer.hpp>
-#include <boost/container/flat_map.hpp>
 #include <boost/container/flat_set.hpp>
 #include <boost/range/iterator_range.hpp>
 #include <nlohmann/json.hpp>
@@ -29,6 +28,7 @@
 #include <xyz/openbmc_project/Inventory/Item/common.hpp>
 
 #include <filesystem>
+#include <flat_map>
 #include <fstream>
 #include <functional>
 #include <map>