Security: dbus: investigate and mitigate command injection

[artiepoole]

Due to the way we are passing arguments along, we should be more careful in testing for side effects when a user tries to call dfx-mgr (or other future softeners).

I see a few tasks/options:

• see how much of an issue this is
• reimplement the dfx-mgr argument parser and require us to maintain it (burden) alongside dfx-mgr upstream
• add fuzz testing
• add side effect tests (try to get around the protections and create files or whatever other harmless, easily detected side effects can be produced and then test against them in future) whackamole style
• rely on an external crate or otherwise get experienced eyes on this

[talhaHavadar]

Fuzz testing is something we should definitely add, regardless

Related: #192

[artiepoole]

I asked copilot to try and do something bad using fpgad. It identified 3 "issues", one of which is just intentional priviledge escalation we use to avoid needing to run cargo as sudo during integration tests.
the other two are:

• Path traversal not blocked (../ is valid) (probably not an issue)
• No size limit on number of inputs / total argument string size (you can send as many valid args as you like)