Bump anaconda from 2025.06 to 2025.12 (#673)

* Bump anaconda from 2025.06 to 2025.12

Bumps anaconda from 2025.06 to 2025.12.

---
updated-dependencies:
- dependency-name: anaconda
  dependency-version: '2025.12'
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

* Temporarily disable build cache for full execution check

* Pin sympy to 1.13.3 to avoid 1.14.0 bug

- SymPy 1.14.0 (bundled with Anaconda 2025.12) has a regression causing
  OverflowError in solve() for symbolic differentiation
- Bug occurs in solow.md when solving c.diff() due to factorint issue
  with large mpz integers trying to convert to float
- Pinning to 1.13.3 which works correctly with Python 3.13
- Added TODO to check for SymPy 1.14.1+ when available

* Re-enable build cache in CI

Re-enabled the _build folder download step now that SymPy 1.13.3
pinning has been applied to fix the execution failure.

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Matt McKay <mmcky@users.noreply.github.com>

Author: dependabot[bot]

environment.yml

@@ -3,7 +3,7 @@ channels:
   - default
 dependencies:
   - python=3.13
-  - anaconda=2025.06
+  - anaconda=2025.12
   - pip
   - pip:
     - jupyter-book==1.0.4post1
@@ -15,5 +15,9 @@ dependencies:
     - sphinxcontrib-youtube==1.4.1
     - sphinx-togglebutton==0.3.2
     - sphinx-reredirects==1.0.0
+    # TODO: Check for SymPy 1.14.1+ when available
+    # Pinned to 1.13.3 due to bug in 1.14.0 causing OverflowError in solve() 
+    # for symbolic differentiation in solow.md (factorint issue with large mpz)
+    - sympy==1.13.3