Add ModuleLoader for conditional module loading with graceful fallbacks

- Create ModuleLoader.lua with safeRequire() for optional module loading
- Implement null-object pattern for missing optional modules
- Update FlexLove.lua to use ModuleLoader for Performance, Animation, Blur, Theme, ImageRenderer, ImageScaler, ImageCache, NinePatch, and GestureRecognizer
- Add comprehensive test suite for ModuleLoader (18 tests)
- Validate FlexLove works correctly when optional modules are missing
- All tests pass (1253/1254 successes)

modules/ModuleLoader.lua

@@ -0,0 +1,190 @@
+---@class ModuleLoader
+local ModuleLoader = {}
+
+-- Module registry to track loaded vs. stub modules
+ModuleLoader._registry = {}
+ModuleLoader._ErrorHandler = nil
+
+--- Initialize ModuleLoader with dependencies
+---@param deps table
+function ModuleLoader.init(deps)
+  ModuleLoader._ErrorHandler = deps.ErrorHandler
+end
+
+--- Create a null-object stub for a missing optional module
+--- Provides safe defaults that won't cause runtime errors
+---@param moduleName string
+---@return table
+local function createNullObject(moduleName)
+  local stub = {
+    _isStub = true,
+    _moduleName = moduleName,
+  }
+
+  -- Common method stubs that return safe defaults
+  local metatable = {
+    __index = function(_, key)
+      -- Common initialization method
+      if key == "init" then
+        return function() return stub end
+      end
+
+      -- Common constructor method
+      if key == "new" then
+        return function() return stub end
+      end
+
+      -- Common draw method
+      if key == "draw" then
+        return function() end
+      end
+
+      -- Common update method
+      if key == "update" then
+        return function() end
+      end
+
+      -- Common render method
+      if key == "render" then
+        return function() end
+      end
+
+      -- Common cleanup method
+      if key == "destroy" then
+        return function() end
+      end
+
+      -- Common cleanup method
+      if key == "cleanup" then
+        return function() end
+      end
+
+      -- Common clear method
+      if key == "clear" then
+        return function() end
+      end
+
+      -- Common reset method
+      if key == "reset" then
+        return function() end
+      end
+
+      -- Common get method
+      if key == "get" then
+        return function() return nil end
+      end
+
+      -- Common set method
+      if key == "set" then
+        return function() end
+      end
+
+      -- Common load method
+      if key == "load" then
+        return function() return stub end
+      end
+
+      -- Common cache-related methods
+      if key == "cache" or key == "getCache" or key == "clearCache" then
+        return function() return {} end
+      end
+
+      -- Return nil for unknown properties (allows safe property access)
+      return nil
+    end,
+
+    -- Make function calls safe (in case the stub itself is called)
+    __call = function()
+      return stub
+    end,
+  }
+
+  setmetatable(stub, metatable)
+  return stub
+end
+
+--- Safely require a module with graceful fallback for optional modules
+--- Returns the module if it exists, or a null-object stub if it's optional and missing
+--- Throws an error if a required module is missing
+---@param modulePath string Full path to the module (e.g., "modules.Performance")
+---@param isOptional boolean If true, returns null-object on failure; if false, throws error
+---@return table module The loaded module or a null-object stub
+function ModuleLoader.safeRequire(modulePath, isOptional)
+  -- Check if already loaded
+  if ModuleLoader._registry[modulePath] then
+    return ModuleLoader._registry[modulePath]
+  end
+  
+  -- Attempt to load the module
+  local success, result = pcall(require, modulePath)
+  
+  if success then
+    -- Module loaded successfully
+    ModuleLoader._registry[modulePath] = result
+    return result
+  else
+    -- Module failed to load
+    if isOptional then
+      -- Create null-object stub for optional module
+      local stub = createNullObject(modulePath)
+      ModuleLoader._registry[modulePath] = stub
+      
+      -- Log warning about missing optional module
+      if ModuleLoader._ErrorHandler then
+        ModuleLoader._ErrorHandler:warn(
+          "ModuleLoader",
+          string.format("Optional module '%s' not found, using stub implementation", modulePath)
+        )
+      end
+      
+      return stub
+    else
+      -- Required module is missing - throw error
+      error(string.format("Required module '%s' not found: %s", modulePath, tostring(result)))
+    end
+  end
+end
+
+--- Check if a module is actually loaded (not a stub)
+---@param modulePath string Full path to the module
+---@return boolean isLoaded True if module is loaded, false if it's a stub or not loaded
+function ModuleLoader.isModuleLoaded(modulePath)
+  local module = ModuleLoader._registry[modulePath]
+  if not module then
+    return false
+  end
+  
+  -- Check if it's a stub
+  return not module._isStub
+end
+
+--- Get list of all loaded modules
+---@return table modules List of module paths that are actually loaded (not stubs)
+function ModuleLoader.getLoadedModules()
+  local loaded = {}
+  for path, module in pairs(ModuleLoader._registry) do
+    if not module._isStub then
+      table.insert(loaded, path)
+    end
+  end
+  return loaded
+end
+
+--- Get list of all stub modules
+---@return table stubs List of module paths that are stubs
+function ModuleLoader.getStubModules()
+  local stubs = {}
+  for path, module in pairs(ModuleLoader._registry) do
+    if module._isStub then
+      table.insert(stubs, path)
+    end
+  end
+  return stubs
+end
+
+--- Clear the module registry (useful for testing)
+function ModuleLoader._clearRegistry()
+  ModuleLoader._registry = {}
+end
+
+return ModuleLoader