Monty 0.0.19 supports open() and with blocks, but a file object is still not
iterable. See pydantic/monty#490, which is still open. The instructions now
state the limitation in three places and give the alternative next to each
one: readlines() or read().split("\n").
Replace chr(10) with "\n" in the prose and in the example. Both work on
0.0.19, and chr(10) implies that the escape is broken.
Add a test that pins the limitation. The test fails when Monty gains
iteration support, which is the signal to relax the instructions.
Document files can be read with open() and with-blocks (.read(),
.readline(), .readlines()); writes raise PermissionError. File objects
remain non-iterable and the collections module is still unavailable.
0.0.19 runs sandboxed code in a subprocess worker pool (AsyncMonty /
AsyncMontySession) and drops MontyRepl. The sandbox checks out a session,
drives it with feed_run, and closes it to return the worker; close() is
now async. Worker crashes surface as a failed SandboxResult. The document
VFS (OSAccess/CallbackFile/MemoryFile) is unchanged.
