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Is your feature request related to a problem? Please describe.
Quickemu as a project aims to "do the right thing" when setting up VMs so they "just work".

This is definitely a valuable goal, but it's such a good software project that it's useful for many use-cases, including situations where a VM is being used to test less-trusted software inside a guest.

In these situations it would be nice to be able to reduce some of the automatically-enabled features of guest VMs with simple boolean toggles in the config file.

Describe the solution you'd like
From what I can tell, the following features are added automatically to the QEMU commandline executed behind the scenes and are not easily toggleable to be "off":

• USB/SPICE redirection (regardless of whether USB passthrough is actually being used)
• USB CCID / Smartcard passthrough (regardless of whether the user actually needs one)
• Folder sharing between host and guest with 9p
• SSH forwarding

In my view, it ought to be reasonably easy to implement a boolean toggle for these options in the config file. Something along the lines of:

usb_redir="false"
usb_ccid="false"
folder_sharing="false"
ssh_fwd="false"

To maintain the "it just works" approach of Quickemu I think the best approach would be to retain the default-on mode of these features, and just document the boolean off toggles for them in the Advanced Features section of the Wiki.

Describe alternatives you've considered
N/A

This approach seems sensible and is not a breaking change as Quickemu will continue to work exactly as before for users who do not enable the above options in their config files.

Additional context
N/A