Refactor genai package to new modular interface

Reorganized the genai package by removing legacy LLM-related files and introducing a new modular interface under the 'interface' directory. Added provider-specific model classes, centralized constants, and updated the example to use the new API and data structures. Updated exports in genai.dart and improved dependency management.

packages/genai/lib/interface/consts.dart

@@ -0,0 +1,71 @@
+import '../consts.dart';
+import '../models/models.dart';
+import 'model_providers/model_providers.dart';
+
+enum ModelAPIProvider { openai, anthropic, gemini, azureopenai, ollama }
+
+final kModelProvidersMap = {
+  ModelAPIProvider.openai: OpenAIModel.instance,
+  ModelAPIProvider.anthropic: AnthropicModel.instance,
+  ModelAPIProvider.gemini: GeminiModel.instance,
+  ModelAPIProvider.azureopenai: AzureOpenAIModel.instance,
+  ModelAPIProvider.ollama: OllamaModel.instance,
+};
+
+const kAnthropicUrl = 'https://api.anthropic.com/v1/messages';
+const kGeminiUrl = 'https://generativelanguage.googleapis.com/v1beta/models';
+const kOpenAIUrl = 'https://api.openai.com/v1/chat/completions';
+const kOllamaUrl = '$kBaseOllamaUrl/v1/chat/completions';
+
+final kDefaultModelRequestData = ModelRequestData(
+  url: '',
+  model: '',
+  apiKey: '',
+  systemPrompt: '',
+  userPrompt: '',
+  modelConfigs: [
+    kDefaultModelConfigTemperature,
+    kDefaultModelConfigTopP,
+    kDefaultModelConfigMaxTokens,
+  ],
+  stream: false,
+);
+
+final kDefaultModelConfigTemperature = ModelConfig(
+  id: 'temperature',
+  name: 'Temperature',
+  description: 'The Temperature of the Model',
+  type: ConfigType.slider,
+  value: ConfigSliderValue(value: (0, 0.5, 1)),
+);
+
+final kDefaultModelConfigTopP = ModelConfig(
+  id: 'top_p',
+  name: 'Top P',
+  description: 'The Top P of the Model',
+  type: ConfigType.slider,
+  value: ConfigSliderValue(value: (0, 0.95, 1)),
+);
+
+final kDefaultModelConfigMaxTokens = ModelConfig(
+  id: 'max_tokens',
+  name: 'Maximum Tokens',
+  description: 'The maximum number of tokens allowed in the output',
+  type: ConfigType.numeric,
+  value: ConfigNumericValue(value: 1024),
+);
+
+final kDefaultModelConfigStream = ModelConfig(
+  id: 'stream',
+  name: 'Enable Streaming Mode',
+  description: 'The LLM output will be sent in a stream instead of all at once',
+  type: ConfigType.boolean,
+  value: ConfigBooleanValue(value: false),
+);
+
+final kDefaultGeminiModelConfigTopP = kDefaultModelConfigTopP.copyWith(
+  id: 'topP',
+);
+
+final kDefaultGeminiModelConfigMaxTokens = kDefaultModelConfigMaxTokens
+    .copyWith(id: 'maxOutputTokens');