Sandbox path-escape check now rejects backslash paths and verifies file identity by inode

What

• The filesystem abstraction gained a statBigint method alongside the existing lstatBigint, for stat calls that follow symlinks with bigint precision.
• The directory-boundary escape check used for sandboxing now explicitly rejects any path containing a backslash, since backslashes make path resolution unreliable.
• After realpath succeeds, the check now also compares the dev/ino (device/inode) values, via the new statBigint, between the original path and its resolved target before declaring it "inside" the sandbox boundary — catching the case where the file was swapped out between resolution and access.

Why This closes a gap where a maliciously crafted or swapped path could appear to resolve inside the sandbox boundary but actually point somewhere else by the time it's accessed; checking file identity by inode, not just by resolved path string, makes the boundary check harder to trick.