fix(types): add missing contentEncoding to S3Options type definition

The runtime support for `contentEncoding` was added in PR #26149 but the
TypeScript type definitions were not updated, causing TS errors and
missing IDE autocompletion.

Closes #27328

Co-Authored-By: Claude <noreply@anthropic.com>

packages/bun-types/s3.d.ts

@@ -299,6 +299,25 @@ declare module "bun" {
      */
     contentDisposition?: string | undefined;
 
+    /**
+     * The Content-Encoding header value.
+     * Specifies what content encodings have been applied to the object,
+     * for example to indicate that it has been compressed.
+     *
+     * @example
+     *    // Setting gzip encoding
+     *     const file = s3.file("data.json.gz", {
+     *       contentEncoding: "gzip"
+     *     });
+     *
+     * @example
+     *    // Setting encoding when writing
+     *     await s3.write("data.json.gz", compressedData, {
+     *       contentEncoding: "gzip"
+     *     });
+     */
+    contentEncoding?: string | undefined;
+
     /**
      * By default, Amazon S3 uses the STANDARD Storage Class to store newly created objects.
      *