mount: Add required rustix features

The bootc-mount crate uses rustix mount, thread, net, fs, and process
modules, but the Cargo.toml was missing these feature declarations.
This causes compilation failures on Linux builds where these features
are required.

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>
Signed-off-by: Eric Curtin <eric.curtin@docker.com>

Author: ericcurtin

crates/mount/Cargo.toml

@@ -17,7 +17,7 @@ anyhow = { workspace = true }
 camino = { workspace = true, features = ["serde1"] }
 fn-error-context = { workspace = true }
 libc = { workspace = true }
-rustix = { workspace = true }
+rustix = { workspace = true, features = ["thread", "net", "fs", "process", "mount"] }
 serde = { workspace = true, features = ["derive"] }
 tracing = { workspace = true }
 tempfile = { workspace = true }