style: use 2-space indentation across entire codebase

Add rustfmt.toml with tab_spaces = 2 and reformat all source files,
tests, and README code examples to use 2-space indentation.

src/models/file.rs

@@ -6,40 +6,40 @@ use serde::Deserialize;
 #[derive(Debug, Clone, Deserialize)]
 #[serde(rename_all = "camelCase")]
 pub struct FileInfo {
-    #[serde(rename = "type")]
-    pub file_type: Option<String>,
-    pub content_type: Option<String>,
-    pub name: Option<String>,
-    pub created_date: Option<DateTime<Utc>>,
-    pub modified_date: Option<DateTime<Utc>>,
-    pub owner: Option<String>,
-    pub notes: Option<String>,
-    pub file_href: Option<String>,
+  #[serde(rename = "type")]
+  pub file_type: Option<String>,
+  pub content_type: Option<String>,
+  pub name: Option<String>,
+  pub created_date: Option<DateTime<Utc>>,
+  pub modified_date: Option<DateTime<Utc>>,
+  pub owner: Option<String>,
+  pub notes: Option<String>,
+  pub file_href: Option<String>,
 }
 
 /// The content of a downloaded file.
 #[derive(Debug, Clone)]
 pub struct FileResponse {
-    pub content_type: Option<String>,
-    pub file_name: Option<String>,
-    pub data: Bytes,
+  pub content_type: Option<String>,
+  pub file_name: Option<String>,
+  pub data: Bytes,
 }
 
 /// Request to upload a file.
 #[derive(Debug, Clone)]
 pub struct SaveFileRequest {
-    pub record_id: i32,
-    pub field_id: i32,
-    pub notes: Option<String>,
-    pub modified_date: Option<DateTime<Utc>>,
-    pub file_name: String,
-    pub file_data: Vec<u8>,
-    pub content_type: String,
+  pub record_id: i32,
+  pub field_id: i32,
+  pub notes: Option<String>,
+  pub modified_date: Option<DateTime<Utc>>,
+  pub file_name: String,
+  pub file_data: Vec<u8>,
+  pub content_type: String,
 }
 
 /// Response from creating a file, containing the new file ID.
 #[derive(Debug, Clone, Deserialize)]
 #[serde(rename_all = "camelCase")]
 pub struct CreatedWithIdResponse {
-    pub id: i32,
+  pub id: i32,
 }