Add base code and examples for the Vertex API

- Add base code for the Vertex API with types and a client with helper
  methods for prompting text and conversation.
- Add examples for prompting text and conversation.

src/types.rs

@@ -0,0 +1,130 @@
+use std::collections::HashMap;
+
+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct CountTokensRequest {
+    pub contents: Content,
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct CountTokensResponse {
+    pub total_tokens: i32,
+}
+
+#[derive(Serialize, Deserialize)]
+pub struct GenerateContentRequest {
+    pub contents: Vec<Content>,
+    pub generation_config: Option<GenerationConfig>,
+    pub tools: Option<Vec<Tools>>,
+}
+
+#[derive(Serialize, Deserialize)]
+pub struct Tools {
+    pub function_declarations: Option<Vec<FunctionDeclaration>>,
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct Content {
+    pub role: String,
+    pub parts: Vec<Part>,
+}
+
+#[derive(Clone, Debug, Serialize, Deserialize, Default)]
+#[serde(rename_all = "camelCase")]
+pub struct GenerationConfig {
+    pub max_output_tokens: Option<i32>,
+    pub temperature: Option<f32>,
+    pub top_p: Option<f32>,
+    pub top_k: Option<i32>,
+    pub stop_sequences: Option<Vec<String>>,
+    pub candidate_count: Option<u32>,
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub enum Part {
+    Text(String),
+    InlineData {
+        mime_type: String,
+        data: String,
+    },
+    FileData {
+        mime_type: String,
+        file_uri: String,
+    },
+    FunctionCall {
+        name: String,
+        args: HashMap<String, String>,
+    },
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct GenerateContentResponse(pub Vec<ResponseStreamChunk>);
+
+#[derive(Debug, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct ResponseStreamChunk {
+    pub candidates: Vec<Candidate>,
+    pub usage_metadata: Option<UsageMetadata>,
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct Candidate {
+    pub content: Content,
+    pub citation_metadata: Option<CitationMetadata>,
+    pub safety_ratings: Vec<SafetyRating>,
+    pub finish_reason: Option<String>,
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct SafetyRating {
+    pub category: String,
+    pub probability: String,
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct Citation {
+    pub start_index: i32,
+    pub end_index: i32,
+    pub uri: String,
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+pub struct CitationMetadata {
+    pub citations: Vec<Citation>,
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct UsageMetadata {
+    pub candidates_token_count: Option<i32>,
+    pub prompt_token_count: i32,
+    pub total_token_count: i32,
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct FunctionDeclaration {
+    pub name: String,
+    pub description: String,
+    pub parameters: FunctionParameters,
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct FunctionParameters {
+    pub r#type: String,
+    pub properties: HashMap<String, FunctionParametersProperty>,
+    pub required: Vec<String>,
+}
+
+#[derive(Debug, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct FunctionParametersProperty {
+    pub r#type: String,
+    pub description: String,
+}