ci: bake cached toolchain into Podman agent and fix nested Buildah [CI]

.woodpecker/dev-image.yml

@@ -26,7 +26,7 @@ steps:
   - name: build-linux-amd64-backend
     image: bash
     environment:
-      NUGET_PACKAGES: /home/justme/.nuget/packages
+      NUGET_PACKAGES: /home/justme/woodpecker/cache/nuget/packages
       ZOT_REGISTRY: registry.oeo.one
       ZOT_USERNAME: justme
       ZOT_SECRET:
@@ -134,7 +134,7 @@ steps:
     when:
       - evaluate: 'not (CI_COMMIT_MESSAGE contains "[SKIP TESTS]")'
     environment:
-      NUGET_PACKAGES: /home/justme/.nuget/packages
+      NUGET_PACKAGES: /home/justme/woodpecker/cache/nuget/packages
     commands:
       - bash ci/verify-backend.sh slow
     depends_on:

.woodpecker/e2e.yml

@@ -26,7 +26,7 @@ steps:
     when:
       - evaluate: 'not (CI_COMMIT_MESSAGE contains "[SKIP TESTS]")'
     environment:
-      NUGET_PACKAGES: /home/justme/.nuget/packages
+      NUGET_PACKAGES: /home/justme/woodpecker/cache/nuget/packages
     commands:
       # 标了 Category=Slow 的端到端测试，见 ci/verify-backend.sh
       - bash ci/verify-backend.sh slow

.woodpecker/linux-release.yml

@@ -31,7 +31,7 @@ steps:
   - name: linux-amd64-backend
     image: bash
     environment:
-      NUGET_PACKAGES: /home/justme/.nuget/packages
+      NUGET_PACKAGES: /home/justme/woodpecker/cache/nuget/packages
       ZOT_REGISTRY: registry.oeo.one
       ZOT_USERNAME: justme
       ZOT_SECRET:
@@ -44,7 +44,7 @@ steps:
   - name: linux-arm64-backend
     image: bash
     environment:
-      NUGET_PACKAGES: /home/justme/.nuget/packages
+      NUGET_PACKAGES: /home/justme/woodpecker/cache/nuget/packages
       ZOT_REGISTRY: registry.oeo.one
       ZOT_USERNAME: justme
       ZOT_SECRET:

.woodpecker/verify.yml

@@ -21,7 +21,7 @@ steps:
     when:
       - evaluate: 'not (CI_COMMIT_MESSAGE contains "[SKIP TESTS]")'
     environment:
-      NUGET_PACKAGES: /home/justme/.nuget/packages
+      NUGET_PACKAGES: /home/justme/woodpecker/cache/nuget/packages
     commands:
       # 增量编译 + 快的那批测试（约 20 秒）；慢的端到端测试在 e2e workflow 里和出镜像并行跑。见 ci/verify-backend.sh
       - bash ci/verify-backend.sh fast