fix(fileutils): resolve UTF-8 encoding incompatibility in multipart form data

Fixes: Encoding::CompatibilityError when sending multipart requests with UTF-8 content
Closes: #528

Author: AaronDDM

.gitignore

@@ -2,6 +2,9 @@
 **/*/.env
 # Example test files
 examples/messages/large_test_file.txt
+examples/messages/small_pdf_test_file.pdf
+examples/messages/large_pdf_test_file.pdf
+examples/messages/large_jpg_test_file.jpg
 *.gem
 *.rbc
 .bundle

CHANGELOG.md

@@ -3,6 +3,7 @@
 ### [Unreleased]
 * Added support for `single_level` query parameter in Folders API for Microsoft accounts
 * Added support for `include_hidden_folders` query parameter in folders list endpoint for Microsoft accounts to control whether hidden folders are included in the response
+* Fix multipart form data encoding compatibility issue with UTF-8 characters in multipart attachment payloads.
 
 ### 6.5.0 / 2025-06-13
 * Replaced `rest-client` dependency with `httparty` for improved maintainability and security