docs: point citation version doi at v2.6.0

Author: dancixx

CITATION.cff

@@ -29,8 +29,8 @@ identifiers:
     value: 10.5281/zenodo.21553307
     description: Concept DOI — always resolves to the latest release.
   - type: doi
-    value: 10.5281/zenodo.21553308
-    description: Version DOI for v2.5.4.
+    value: 10.5281/zenodo.21620281
+    description: Version DOI for v2.6.0.
 keywords:
   - quantitative finance
   - stochastic processes