terminal: change OSC parser to explicit init to set undefined

This works around: https://github.com/ziglang/zig/issues/19148
This lets our `test-valgrind` command catch some issues. We'll have to
follow this pattern in more places but I want to do it incrementally so
things keep passing.

I **do not** want to blindly follow this pattern everywhere. I want to
start by focusing in only on the structs that set `undefined` as default
fields that we're also about to test in isolation with Valgrind. Its
just too much noise otherwise and not a general style I'm sure of; it's
worth it for Valgrind though.

.github/workflows/test.yml

@@ -22,7 +22,6 @@ jobs:
       - build-macos-matrix
       - build-windows
       - flatpak-check-zig-cache
-      - flatpak
       - test
       - test-gtk
       - test-gtk-ng
@@ -1013,28 +1012,29 @@ jobs:
       - name: Check Flatpak Zig Dependencies
         run: nix develop -c ./flatpak/build-support/check-zig-cache.sh
 
-  flatpak:
-    if: github.repository == 'ghostty-org/ghostty'
-    name: "Flatpak"
-    container:
-      image: ghcr.io/flathub-infra/flatpak-github-actions:gnome-47
-      options: --privileged
-    strategy:
-      fail-fast: false
-      matrix:
-        variant:
-          - arch: x86_64
-            runner: namespace-profile-ghostty-md
-          - arch: aarch64
-            runner: namespace-profile-ghostty-md-arm64
-    runs-on: ${{ matrix.variant.runner }}
-    needs: [flatpak-check-zig-cache, test]
-    steps:
-      - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
-      - uses: flatpak/flatpak-github-actions/flatpak-builder@10a3c29f0162516f0f68006be14c92f34bd4fa6c # v6.5
-        with:
-          bundle: com.mitchellh.ghostty
-          manifest-path: flatpak/com.mitchellh.ghostty.yml
-          cache-key: flatpak-builder-${{ github.sha }}
-          arch: ${{ matrix.variant.arch }}
-          verbose: true
+  # Disabled until we update to Zig 0.15 or if we can pin this to Zig 0.14
+  # flatpak:
+  #   if: github.repository == 'ghostty-org/ghostty'
+  #   name: "Flatpak"
+  #   container:
+  #     image: ghcr.io/flathub-infra/flatpak-github-actions:gnome-47
+  #     options: --privileged
+  #   strategy:
+  #     fail-fast: false
+  #     matrix:
+  #       variant:
+  #         - arch: x86_64
+  #           runner: namespace-profile-ghostty-md
+  #         - arch: aarch64
+  #           runner: namespace-profile-ghostty-md-arm64
+  #   runs-on: ${{ matrix.variant.runner }}
+  #   needs: [flatpak-check-zig-cache, test]
+  #   steps:
+  #     - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
+  #     - uses: flatpak/flatpak-github-actions/flatpak-builder@10a3c29f0162516f0f68006be14c92f34bd4fa6c # v6.5
+  #       with:
+  #         bundle: com.mitchellh.ghostty
+  #         manifest-path: flatpak/com.mitchellh.ghostty.yml
+  #         cache-key: flatpak-builder-${{ github.sha }}
+  #         arch: ${{ matrix.variant.arch }}
+  #         verbose: true