Merge remote-tracking branch 'upstream/main' into feature/mixedPolytrope

# Conflicts:
#	.gitignore
#	build-config/meson.build
#	meson.build
#	meson_options.txt
#	src/composition/public/composition.h
#	src/config/public/config.h
#	src/constants/public/const.h
#	src/meson.build
#	tests/composition_sandbox/comp.cpp

src/constants/public/const.h

@@ -20,9 +20,7 @@
 // *********************************************************************** */
 #pragma once
 #include <string>
-#include <fstream>
 #include <iostream>
-#include <vector>
 #include <set>
 #include <map>
 
@@ -95,7 +93,7 @@ private:
 public:
 
   /**
-   * @brief get instance of constants singelton
+   * @brief get instance of constants singleton
    * @return instance of constants
    */
   static Constants& getInstance() {
@@ -107,7 +105,7 @@ public:
    * @brief Check if constants are loaded.
    * @return True if constants are loaded, false otherwise.
    */
-  bool isLoaded() { return loaded_; }
+  bool isLoaded() const { return loaded_; }
 
   /**
    * @brief Get a constant by key.