Make a decision on chdir support

The core LiteBox crate itself internally maintains (in some of its file systems) a notion of cwd, but it does not actually expose a chdir or similar, since the cwd support is not fully matured. For now, #692 is introducing chdir at the shim layer, but we need to think about whether some version of this should be at the LiteBox layer, or if we want to just rip out the cwd support inside LiteBox entirely.

Start by reviewing the core LiteBox crate's current cwd support and the shim-layer chdir work in #692. Compare whether cwd should be exposed at the LiteBox layer or removed internally; done means recording a clear decision and its resulting direction.

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