Add inode limits to tmpfs

[wookie184]

Adding an inode limit would limit the number of files/directories that can exist in the tmpfs we use for file IO. Given we already have file size limits, a maximum number of files we'll read, and a timeout, it shouldn't be too important, but it may be worth putting a limit to be safe. Currently it seems to be limited by the cgroup memory limit using (allowing for about 50_000 files with the current config).

This can be done by passing the nr_inodes argument here:

snekbox/snekbox/memfs.py

Line 58 in afda301

mount("", self.path, "tmpfs", size=self.instance_size)

[jb3]

We should probably add a similar nr_inodes limit for the tmpfs we spawn for /dev/shm. This would be specified in the nsjail config file though. See #113.