restructure into smaller files & add IWYU/clang-tidy

Signed-off-by: Folling <mail@folling.io>

include/ikarus/folders/blueprint_folder.h

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+#pragma once
+
+/// \file blueprint_folder.h
+/// \author Folling <mail@folling.io>
+
+#include <ikarus/id.h>
+#include <ikarus/macros.h>
+
+/// \addtogroup folder Folders
+/// @{
+
+IKARUS_BEGIN_HEADER
+
+/// \brief A blueprint folder, storing blueprints and other blueprint folders.
+struct IkarusBlueprintFolder {
+    /// \private \brief The id of the blueprint folder.
+    IkarusId id;
+};
+
+IKARUS_END_HEADER
+
+// @}

include/ikarus/folders/entity_folder.h

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+#pragma once
+
+/// \file entity_folder.h
+/// \author Folling <mail@folling.io>
+
+#include <ikarus/id.h>
+#include <ikarus/macros.h>
+
+/// \addtogroup folder Folders
+/// @{
+
+IKARUS_BEGIN_HEADER
+
+/// \brief A entity folder, storing entities and other entity folders.
+struct IkarusEntityFolder {
+    /// \private \brief The id of the entity folder.
+    IkarusId id;
+};
+
+IKARUS_END_HEADER
+
+// @}

include/ikarus/folders/folder.h

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+#pragma once
+
+/// \file folder.h
+/// \author Folling <mail@folling.io>
+
+#include <ikarus/folders/blueprint_folder.h>
+#include <ikarus/folders/entity_folder.h>
+#include <ikarus/folders/folder_type.h>
+#include <ikarus/folders/property_folder.h>
+#include <ikarus/macros.h>
+
+IKARUS_BEGIN_HEADER
+
+/// \defgroup folder Folders
+/// \brief Folders are used to group objects together.
+/// @{
+
+/// \private \brief The data of a folder.
+union IkarusFolderData {
+    /// \private \brief The blueprint folder data of the folder.
+    IkarusBlueprintFolder blueprint_folder;
+    /// \private \brief The property folder data of the folder.
+    IkarusPropertyFolder property_folder;
+    /// \private \brief The entity folder data of the folder.
+    IkarusEntityFolder entity_folder;
+};
+
+/// \brief A generic folder. Similar to how Objects wrap all types of objects, Folders wrap all types of folders.
+struct IkarusFolder {
+    /// \private \brief The data of the folder.
+    IkarusFolderData data;
+
+    /// \private \brief The type of the folder.
+    IkarusFolderType type;
+};
+
+/// \brief Constructs a folder from a blueprint folder.
+/// \param blueprint_folder The blueprint folder to construct the folder from.
+/// \return The constructed folder.
+IKA_API IkarusFolder ikarus_folder_from_blueprint_folder(IkarusBlueprintFolder blueprint_folder);
+/// \brief Constructs a folder from a property folder.
+/// \param property_folder The property folder to construct the folder from.
+/// \return The constructed folder.
+IKA_API IkarusFolder ikarus_folder_from_property_folder(IkarusPropertyFolder property_folder);
+/// \brief Constructs a folder from an entity folder.
+/// \param entity_folder The entity folder to construct the folder from.
+/// \return The constructed folder.
+IKA_API IkarusFolder ikarus_folder_from_entity_folder(IkarusEntityFolder entity_folder);
+
+/// \brief Fetches the folder type of a folder.
+/// \param folder The folder to fetch the type of.
+/// \return The type of the folder.
+IKA_API IkarusFolderType ikarus_folder_get_type(IkarusFolder folder);
+
+/// \brief Checks if two folders are equal.
+/// \details Since ids store the type of the object, this boils down to a simple comparison of the ids.
+/// \param left The left side of the comparison.
+/// \param right The right side of the comparison.
+/// \return True if the folders are equal, false otherwise
+IKA_API bool ikarus_folder_is_equal(IkarusFolder left, IkarusFolder right);
+
+/// \brief Visits a folder. Calling the appropriate function for the folder's type.
+/// \param folder The folder to visit.
+/// \param blueprint The function to call if the folder is a blueprint folder.
+/// \param property The function to call if the folder is a property folder.
+/// \param entity The function to call if the folder is an entity folder.
+/// \param data The data to pass to the functions.
+IKA_API void ikarus_folder_visit(
+    IkarusFolder folder,
+    void (*blueprint)(IkarusBlueprintFolder, void *),
+    void (*property)(IkarusPropertyFolder, void *),
+    void (*entity)(IkarusEntityFolder, void *),
+    void * data
+);
+
+IKARUS_END_HEADER

include/ikarus/folders/folder_type.h

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+#pragma once
+
+// IMPLEMENTATION_DETAIL_FOLDER_TYPES
+
+/// \file folder_type.h
+/// \author Folling <mail@folling.io>
+
+#include <ikarus/macros.h>
+
+/// \addtogroup folder folders
+/// @{
+
+/// \brief The type of an folder.
+/// \remark Folders have the 8th bit set.
+enum IkarusFolderType {
+    /// \brief Not a folder or no folder.
+    IkarusFolderType_None = 0,
+    /// \brief An IkarusBlueprintFolder
+    IkarusFolderType_BlueprintFolder = 0b1000'0001,
+    /// \brief An IkarusPropertyFolder
+    IkarusFolderType_PropertyFolder = 0b1000'0010,
+    /// \brief An IkarusEntityFolder
+    IkarusFolderType_EntityFolder = 0b1000'0011,
+};
+
+/// @}

include/ikarus/folders/property_folder.h

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+#pragma once
+
+#include <ikarus/id.h>
+#include <ikarus/macros.h>
+
+/// \file property_folder.h
+/// \author Folling <mail@folling.io>
+
+/// \addtogroup folder Folders
+/// @{
+
+IKARUS_BEGIN_HEADER
+
+/// \brief A property folder, storing properties and other property folders.
+/// \remark Property folders are scoped to the blueprint or entity they are associated with.
+struct IkarusPropertyFolder {
+    /// \private \brief The id of the property folder.
+    IkarusId id;
+};
+
+IKARUS_END_HEADER
+
+// @}