rng ranges: Forbid use of panicky Rng::gen_range

Fixes #920

clippy.toml

@@ -1,3 +1,4 @@
 disallowed-methods = [
+    { path = "rand::Rng::gen_range", reason = "Prefer tor_basic_utils::RngExt::gen_range_checked to avoid uncontrolled panics, or gen_range_infallible if applicable" },
 #    { path = "std::time::SystemTime::now", reason = "prefer using SleepProvider::wallclock instead when possible" },
 ]

crates/tor-basic-utils/src/lib.rs

@@ -123,6 +123,7 @@ pub trait RngExt: Rng {
         if range.is_empty() {
             None
         } else {
+            #[allow(clippy::disallowed_methods)]
             Some(Rng::gen_range(self, range))
         }
     }