Require the backend release that fixes the handle and arity defects

sparse-ir 2.1.5 and pylibsparseir 0.10.0 are on PyPI. Below those the
notebooks still run, but 0.9.1 floods several of them with warnings from
finalizers that release a handle the wrapper does not own
(SpM-lab/sparse-ir-rs#282), so the floor moves up rather than staying at a
version whose output nobody wants to publish.

The notebooks produce the same numbers on either stack: every output cell of
all 19 notebooks was compared between 2.1.4/0.9.1 and 2.1.5/0.10.0 and is
identical apart from matplotlib object addresses.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: shinaoka

pyproject.toml

@@ -7,7 +7,7 @@ dependencies = [
     "matplotlib",
     "ghp-import",
     "jupyterlab",
-    "sparse-ir>=2.0.0a9",
+    "sparse-ir>=2.1.5",
     "admmsolver",
-    "pylibsparseir>=0.7.5",
+    "pylibsparseir>=0.10.0",
 ]