fix: parse errors

```
/test/memory_resources/_memory_resources.cxx: In member function ‘virtual void {anonymous}::MemoryResources_allocator_Test::TestBody()’:
/test/memory_resources/_memory_resources.cxx:104:12: error: parse error in template argument list
  104 |     config.SetProperty<string>("session", to_string(session));
      |            ^~~~~~~~~~~~~~~~~~~
/test/memory_resources/_memory_resources.cxx:104:31: error: no matching function for call to ‘fair::mq::ProgOptions::SetProperty<<expression error> >(const char [8], std::string)’
  104 |     config.SetProperty<string>("session", to_string(session));
      |     ~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /home/dklein/projects/FairMQ2/test/memory_resources/_memory_resources.cxx:11:
/fairmq/ProgOptions.h:269:6: note: candidate: ‘template<class T> void fair::mq::ProgOptions::SetProperty(const std::string&, T)’
  269 | void fair::mq::ProgOptions::SetProperty(const std::string& key, T val)
      |      ^~~~
/fairmq/ProgOptions.h:269:6: note:   template argument deduction/substitution failed:
/test/memory_resources/_memory_resources.cxx:104:31: error: template argument 1 is invalid
  104 |     config.SetProperty<string>("session", to_string(session));
      |     ~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/test/memory_resources/_memory_resources.cxx: In member function ‘virtual void {anonymous}::MemoryResources_getMessage_Test::TestBody()’:
/test/memory_resources/_memory_resources.cxx:132:12: error: parse error in template argument list
  132 |     config.SetProperty<string>("session", to_string(session));
      |            ^~~~~~~~~~~~~~~~~~~
/test/memory_resources/_memory_resources.cxx:132:31: error: no matching function for call to ‘fair::mq::ProgOptions::SetProperty<<expression error> >(const char [8], std::string)’
  132 |     config.SetProperty<string>("session", to_string(session));
      |     ~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/fairmq/ProgOptions.h:269:6: note: candidate: ‘template<class T> void fair::mq::ProgOptions::SetProperty(const std::string&, T)’
  269 | void fair::mq::ProgOptions::SetProperty(const std::string& key, T val)
      |      ^~~~
/fairmq/ProgOptions.h:269:6: note:   template argument deduction/substitution failed:
/test/memory_resources/_memory_resources.cxx:132:31: error: template argument 1 is invalid
  132 |     config.SetProperty<string>("session", to_string(session));
      |     ~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```

fairmq/MemoryResources.h

@@ -17,7 +17,7 @@
 
 #include <boost/container/container_fwd.hpp>
 #include <boost/container/flat_map.hpp>
-#include <boost/container/pmr/memory_resource.hpp>
+#include <memory_resource>
 #include <cstring>
 #include <fairmq/Message.h>
 #include <stdexcept>
@@ -27,7 +27,7 @@ namespace fair::mq {
 
 class TransportFactory;
 using byte = unsigned char;
-namespace pmr = boost::container::pmr;
+namespace pmr = std::pmr;
 
 /// All FairMQ related memory resources need to inherit from this interface
 /// class for the

test/memory_resources/_memory_resources.cxx

@@ -16,6 +16,7 @@
 #include <gtest/gtest.h>
 
 #include <cstring>
+#include <string>
 #include <vector>
 
 namespace
@@ -101,7 +102,7 @@ TEST(MemoryResources, allocator)
 
     size_t session{tools::UuidHash()};
     ProgOptions config;
-    config.SetProperty<string>("session", to_string(session));
+    config.SetProperty<std::string>("session", to_string(session));
 
     FactoryType factoryZMQ = TransportFactory::CreateTransportFactory("zeromq", fair::mq::tools::Uuid(), &config);
 
@@ -129,7 +130,7 @@ TEST(MemoryResources, getMessage)
 
     size_t session{tools::UuidHash()};
     ProgOptions config;
-    config.SetProperty<string>("session", to_string(session));
+    config.SetProperty<std::string>("session", to_string(session));
     config.SetProperty<bool>("shm-monitor", true);
 
     FactoryType factoryZMQ = TransportFactory::CreateTransportFactory("zeromq", fair::mq::tools::Uuid(), &config);