docs: narrow the changelog precision claim

Address review: the fix moved the learning-rate/tree-value product and the
forest accumulation to double, but individual tree values are still f32. Say
that precisely instead of claiming the whole prediction is computed in double.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: mstrathman

CHANGELOG.md

@@ -9,11 +9,12 @@ project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 ### Fixed
 
 - **Forest prediction accumulates the learning-rate product in double**, matching
-  the trainer. The serving path computed `float * float` before widening to the
-  `double` accumulator, which could overflow to infinity (and, under x87 excess
-  precision, differ by platform) before the widening. Predictions are computed
-  consistently in double now; served values may shift in their least-significant
-  digits.
+  the trainer. The serving path multiplied the learning rate by a tree value as
+  `float * float` before widening to the `double` accumulator, which could
+  overflow to infinity (and, under x87 excess precision, differ by platform)
+  before the widening. The product and the forest accumulation are now computed in
+  double (individual tree values are still `f32`); served predictions may shift in
+  their least-significant digits.
 
 ## [0.2.0] - 2026-07-31