ci: restore build cache for PR CI, with A2 wheel fix

[JavaPythonAIForBAT]

Summary

#479 rolled back the PR-side cache wiring after #469's cache scheme broke test-build-deepep-a2. The push-side workflow file (push_build_cache.yml) was kept on main but still has the original bugs. This PR reintroduces the cache for PR CI with both bugs fixed and the CANN-version mismatch resolved.

push_build_cache.yml

• A2 build now runs bash build.sh -a deepep2. The bare invocation defaults to BUILD_DEEPEP_OPS=ON + SOC_VERSION=Ascend910_9382, i.e. an A3 wheel — so the A2 cache entry used to contain an A3 wheel, which is what caused test-build-deepep-a2 to fail when restoring from the cache.
• Rename Build step labels to Build (a3) / Build (a2). The previous deepep2 for a3 was self-contradictory.
• Bump cache key v1 → v2 so already-poisoned v1 entries on main are not reused.

pr-test-npu.yml

• Re-add Get build hash / Restore build cache to test-all-build, test-build-deepep-a3, test-build-deepep-a2.
• Prepare Deepep skips bash build.sh and installs the cached wheel when cache-hit; otherwise falls back to the original prepare_deepep_in_container.sh path.
• Cache keys use v2 and the CANN tag in the key (cann8.5.0) matches both push_build_cache.yml's container and pr-test-npu.yml's containers on current main (after rollback build cache and cann 9.0.0 #479).

No container images, test definitions, or other workflows are touched.

Test plan

• First PR after merge: all three NPU jobs cache-miss on v2, fall back to prepare_deepep_in_container.sh, and succeed
• After a subsequent main push, push_build_cache.yml populates v2 entries for both A3 and A2 (note: A2 entry is now an actual A2 wheel)
• A later PR run hits the v2 cache; test-build-deepep-a2 installs the A2 wheel and tests pass
• No regression in test-all-build / test-build-deepep-a3 cache reuse (both share the a3 cache key, both install only deep_ep*.whl)

🤖 Generated with Claude Code

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Note

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[JavaPythonAIForBAT]

关于 CI 失败

test_internode_a2 失败原因

当前 multi-node (test_internode_a2, 2, tests/python/deepep/test_internode_a2.py) / test_internode_a2 失败的根本原因是：

fatal: not a git repository (or any of the parent directories): .git

这是 internode.yml workflow 在构建 deepep 时试图更新 git submodule（third-party/pto-isa），但当前工作目录不是 git repo 导致的。这个问题与本 PR 的 cache key 改动无关，是预先存在的 bug。

Cache key 改动已完成

已在 commit aca45f4 中实现：

• ✅ 移除了 YAML 中的硬编码 cann8.5.0- 字面量
• ✅ 在运行时从容器内 /usr/local/Ascend/ascend-toolkit/latest/version.cfg 动态派生 CANN 版本
• ✅ 所有 5 个 cache key（pr-test-npu.yml × 3，push_build_cache.yml × 2）都已更新
• ✅ 版本来源现在完全由 image: 字段控制，消除了第二份真相源

这样既满足了"不硬编码版本"的要求，又保留了 cache key 中的版本维度，防止跨 CANN 版本的缓存误用。

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关于 internode 测试失败，建议单独提 issue 或 PR 来修复 deepep 构建脚本的 git repo 依赖问题。