⬆️ version bump to v4.5

- Update obioptions.Version from "Release 4.4.29" to "/v/ Release v5"
- Update version.txt from 4.29 → .30
(automated by Makefile)

autodoc/docmd/pkg/obistats/mathx.md

@@ -0,0 +1,27 @@
+# `obistats` Package: Semantic Overview
+
+The `obistats` package provides low-level statistical and combinatorial utilities in pure Go, focusing on numerical robustness and performance.
+
+- **Sign Function (`mathSign`)**  
+  Returns the sign of a `float64`: `-1`, `0`, or `+1`. Handles NaN by returning NaN.
+
+- **Precomputed Factorials (`smallFact`)**  
+  Precomputes factorials from `0!` to `20!` (fits in 64-bit signed integer), enabling fast exact binomial coefficient computation for small `n`.
+
+- **Binomial Coefficient (`mathChoose`)**  
+  Computes $\binom{n}{k}$ efficiently:
+  - For `n ≤ 20`: uses integer arithmetic (multiplication + division) for exact results.
+  - For larger `n`: leverages logarithms via `mathLchoose` and exponentiates (`exp(log(Choose))`) to avoid overflow.
+
+- **Log-Binomial Coefficient (`mathLchoose`)**  
+  Computes $\log \binom{n}{k}$ via the log-gamma function:  
+  $$\log \binom{n}{k} = \lg(n+1) - \lg(k+1) - \lg(n-k+1)$$  
+  Ensures numerical stability for large `n`, avoiding overflow/underflow.
+
+- **Internal Helper (`lchoose`)**  
+  Core implementation of log-binomial using `math.Lgamma`, reused by both exact and large-scale paths.
+
+**Design Notes**:  
+- Prioritizes correctness (e.g., NaN propagation, edge-case handling).  
+- Balances speed and precision: exact integer arithmetic for small inputs; log-space computation for scalability.  
+- Mirrors functionality from an internal benchmarking module, adapted here as a standalone utility.