feat: initial implementation of creating a file via the Files API

src/AnthropicClient/Models/AnthropicFile.cs

@@ -0,0 +1,53 @@
+using System.Text.Json.Serialization;
+
+namespace AnthropicClient.Models;
+
+/// <summary>
+/// Represents a file object from the Anthropic Files API.
+/// </summary>
+public class AnthropicFile
+{
+  /// <summary>
+  /// Unique object identifier.
+  /// The format and length of IDs may change over time.
+  /// </summary>
+  [JsonPropertyName("id")]
+  public string Id { get; init; } = string.Empty;
+
+  /// <summary>
+  /// Object type.
+  /// For files, this is always "file".
+  /// </summary>
+  [JsonPropertyName("type")]
+  public string Type { get; init; } = "file";
+
+  /// <summary>
+  /// Original filename of the uploaded file.
+  /// </summary>
+  [JsonPropertyName("file_name")]
+  public string FileName { get; init; } = string.Empty;
+
+  /// <summary>
+  /// RFC 3339 datetime string representing when the file was created.
+  /// </summary>
+  [JsonPropertyName("created_at")]
+  public string CreatedAt { get; init; } = string.Empty;
+
+  /// <summary>
+  /// Size of the file in bytes.
+  /// </summary>
+  [JsonPropertyName("size_bytes")]
+  public long SizeBytes { get; init; }
+
+  /// <summary>
+  /// MIME type of the file.
+  /// </summary>
+  [JsonPropertyName("file_type")]
+  public string FileType { get; init; } = string.Empty;
+
+  /// <summary>
+  /// Whether the file can be downloaded.
+  /// </summary>
+  [JsonPropertyName("downloadable")]
+  public bool Downloadable { get; init; }
+}