Update from rand 0.8 to 0.9

Reviewed By: diliop

Differential Revision: D99613510

fbshipit-source-id: 1a1f8a73ff7e2b34795287451122dcc6bdc32879

Author: David Tolnay

below/btrfs/Cargo.toml

@@ -15,8 +15,8 @@ common = { package = "below-common", version = "0.11.0", path = "../common" }
 libc = "0.2.183"
 nix = { version = "0.30.1", features = ["dir", "event", "hostname", "inotify", "ioctl", "mman", "mount", "net", "poll", "ptrace", "reboot", "resource", "sched", "signal", "term", "time", "user", "zerocopy"] }
 openat = "0.1.21"
-rand = { version = "0.8", features = ["small_rng"] }
-rand_distr = "0.4.3"
+rand = { version = "0.9", features = ["small_rng"] }
+rand_distr = "0.5"
 serde = { version = "1.0.219", features = ["derive", "rc"] }
 slog = { version = "2.8.2", features = ["max_level_trace", "nested-values"] }
 thiserror = "2.0.18"

below/btrfs/src/lib.rs

@@ -257,8 +257,8 @@ impl BtrfsReader {
         .map_err(Error::SysError)?;
 
         let mut roots = Roots::new(fd);
-        let uniform = Uniform::new(0, total_chunk_length);
-        let mut rng = rand::thread_rng();
+        let uniform = Uniform::new(0, total_chunk_length).unwrap();
+        let mut rng = rand::rng();
 
         let mut sample_tree = SampleTree::new();
         let mut total_samples = 0;