Bump jupyter-book from 1.0.4post1 to 2.1.0

Bumps [jupyter-book](https://github.com/jupyter-book/jupyter-book) from 1.0.4post1 to 2.1.0.
- [Release notes](https://github.com/jupyter-book/jupyter-book/releases)
- [Commits](jupyter-book/jupyter-book@v1.0.4.post1...v2.1.0)

---
updated-dependencies:
- dependency-name: jupyter-book
  dependency-version: 2.1.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

environment.yml

@@ -6,7 +6,7 @@ dependencies:
   - anaconda=2025.06
   - pip
   - pip:
-    - jupyter-book==1.0.4post1
+    - jupyter-book==2.1.0
     - quantecon-book-theme==0.9.2
     - sphinx-tojupyter==0.3.1
     - sphinxext-rediraffe==0.2.7