[meson] add boost as dependency

I setup a new development environment and emper did not compile because
emper::io::Stats use the circular_buffer provided by boost.
Boost was not installed and our build-system failed to detect it.

This change adds the header-only boost dependency to emper.
https://mesonbuild.com/Dependencies.html#boost
The header-only dependency is enough to build emper default configuration.

When linking against boost is required we use the 'modules' karg.

meson.build

@@ -19,7 +19,11 @@ if not uring_dep.found()
 endif
 
 numa_dep = dependency('numa')
-emper_dependencies = [thread_dep, uring_dep, numa_dep]
+
+# boost header dependency needed for the circular_buffer used in emper/io/Stats.cpp
+boost_dep = dependency('boost')
+
+emper_dependencies = [thread_dep, uring_dep, numa_dep, boost_dep]
 
 boost_thread_dep = dependency('boost', modules : ['thread'], required: false)