* Add request.form() for multipart form data and file uploads
New Request.form() method that handles both application/x-www-form-urlencoded
and multipart/form-data content types with streaming parsing.
Features:
- Streaming multipart parser that doesn't buffer entire body in memory
- Files spill to disk above 1MB threshold via SpooledTemporaryFile
- files=False (default) discards file content, files=True stores them
- Security limits: max_request_size, max_file_size, max_fields, max_files
- FormData container with dict-like access and getlist() for multiple values
- UploadedFile class with async read(), seek(), filename, content_type, size
- Support for RFC 5987 filename* encoding for international filenames
Uses multipart-form-data-conformance test suite for validation.
* Update views to use request.form() and document new API
- Migrate PermissionsDebugView, MessagesDebugView, and CreateTokenView
from post_vars() to form()
- Add documentation for request.form(), FormData, and UploadedFile classes
Centralize multipart defaults and expose stricter limits via Request.form().
Enforce header, part, file, and disk space limits even when files are discarded; detect truncated bodies and client disconnects; and move blocking work off the event loop.
Add FormData close/aclose context managers, update internals docs, and expand multipart tests (including len semantics and stricter conformance expectations).
