Bring over gmres from pytential, build_matrix from sumpy

Author: inducer

.github/workflows/ci.yml

@@ -38,7 +38,7 @@ jobs:
         -   uses: actions/checkout@v6
         -   name: "Main Script"
             run: |
-                EXTRA_INSTALL="pytest types-colorama types-Pygments scipy-stubs"
+                EXTRA_INSTALL="pytest types-colorama types-Pygments scipy-stubs matplotlib"
                 curl -L -O https://tiker.net/ci-support-v0
                 . ./ci-support-v0