Fix MultiConfiguredPC.hxx compilation with C++20 (#737)

Due to the C++20 standard removing the construct and destruct methods from std::allocator, it was necessary to adjust the code to use std::allocator_traits instead which has provided these methods since C++11.

Fixes #711

===

* Fix MultiConfiguredPC.hxx compilation with C++20

C++20 removed the construct / destruct methods from std::allocator with the replacement methods being part of std::allocator_traits intead.

Fixes #711

* Update MultiConfiguredPC.hxx

Fix missing }

* Update MultiConfiguredPC.hxx

Due to the C++20 standard removing the construct and destruct methods from std::allocator, it was necessary to adjust the code to use std::allocator_traits instead which has provided these methods since C++11.

src/openlcb/MultiConfiguredPC.hxx

@@ -41,6 +41,7 @@
 #include "openlcb/RefreshLoop.hxx"
 #include "utils/ConfigUpdateListener.hxx"
 #include "utils/ConfigUpdateService.hxx"
+#include "utils/Debouncer.hxx"
 #include "utils/format_utils.hxx"
 
 namespace openlcb
@@ -141,7 +142,7 @@ public:
         debouncers_ = alloc.allocate(size_);
         for (unsigned i = 0; i < size_; ++i)
         {
-            alloc.construct(debouncers_ + i, 3);
+            alloc_traits::construct(alloc, debouncers_ + i, 3);
         }
     }
 
@@ -153,7 +154,7 @@ public:
         std::allocator<debouncer_type> alloc;
         for (unsigned i = 0; i < size_; ++i)
         {
-            alloc.destroy(debouncers_ + i);
+            alloc_traits::destroy(alloc, debouncers_ + i);
         }
         alloc.deallocate(debouncers_, size_);
     }
@@ -336,6 +337,8 @@ public:
     }
 
 private:
+    using alloc_traits = std::allocator_traits<std::allocator<debouncer_type>>;
+
     /// Removes registration of this event handler from the global event
     /// registry.
     void do_unregister()