Enhance utilities documentation with additional date and random number examples

docs/src/utilities.md

@@ -3,16 +3,36 @@
 Utilities provide handy helpers around the core library. Existing tools
 include:
 
-- Date utilities for generating calendar sequences.
+- Date utilities for generating calendar sequences and business‑day sets
+- Random number generators for simulations and testing
 
 ## Date Helpers
 
 ```rust
 # extern crate rustframe;
-use rustframe::utils::dateutils::{DatesList, DateFreq};
+use rustframe::utils::dateutils::{BDatesList, BDateFreq, DatesList, DateFreq};
 
+// Calendar sequence
 let list = DatesList::new("2024-01-01".into(), "2024-01-03".into(), DateFreq::Daily);
 assert_eq!(list.count().unwrap(), 3);
+
+// Business days starting from 2024‑01‑02
+let bdates = BDatesList::from_n_periods("2024-01-02".into(), BDateFreq::Daily, 3).unwrap();
+assert_eq!(bdates.list().unwrap().len(), 3);
+```
+
+## Random Numbers
+
+The `random` module offers deterministic and cryptographically secure RNGs.
+
+```rust
+# extern crate rustframe;
+use rustframe::random::{Prng, Rng};
+
+let mut rng = Prng::new(42);
+let v1 = rng.next_u64();
+let v2 = rng.next_u64();
+assert_ne!(v1, v2);
 ```
 
 Upcoming utilities will cover: