Reuse Blender 5.2.0 dependencies across ARM64 patch builds

[michaelgold]

Summary

• map every Blender 5.2.x Linux ARM64 build to the immutable 5.2.0 dependency release
• verify shared bundle provenance against the Blender v5.2.0 tag commit
• keep cache and release identities series-stable while preventing patch builds from poisoning or publishing the base cache/bundle
• preserve native fallback and exact requested wheel-version validation

Regression evidence

The failed v5.2.1 run requested deps-blender-5.2.1-linux-arm64-v1, received 404, rebuilt dependencies for six hours, and timed out. This change makes it request deps-blender-5.2.0-linux-arm64-v1.

Verification

• 38 tests pass on CPython 3.13.12
• no-tools simulation: 24 pass, 14 tool-dependent tests skip
• Python compilation and workflow YAML parsing pass
• exact-diff specification and security/correctness reviews: zero findings

[Copilot]

🟢 Approval recommended

The changes align with the stated goal (reuse 5.2.0 deps for 5.2.x ARM64 builds) and include targeted tests, with only a minor documentation formatting issue noted.

Pull request overview

This PR ensures Linux ARM64 builds for Blender 5.2.x reuse the immutable Blender 5.2.0 dependency bundle (release + cache identity), preventing patch releases (e.g., 5.2.1) from triggering expensive native rebuilds while still validating the wheel against the exact requested Blender version.

Changes:

• Added a semantic-version–validated dependency bundle selector that maps Blender 5.2.x to dependency version 5.2.0.
• Updated Linux ARM64 build logic and workflow caching/publishing rules to reuse the 5.2.0 bundle across 5.2 patch builds while keeping native fallback behavior.
• Expanded tests to cover bundle selection rules, rejection of non-semver inputs, and end-to-end patch reuse behavior.

File summaries

File	Description
tests/test_arm64_deps_bundle.py	Adds unit + integration coverage for 5.2.x → 5.2.0 bundle selection, semver validation, and patch build reuse behavior.
src/buildbpy/main.py	Switches ARM64 bundle resolution to the selector and verifies bundle provenance against the correct Blender tag commit.
src/buildbpy/arm64_deps.py	Introduces BundleSpec.for_blender_version() to enforce semver input and map 5.2 patch releases to 5.2.0 dependencies.
README.md	Documents 5.2.x reuse and immutability behavior for ARM64 dependency bundles.
.github/workflows/build_linux_arm64.yml	Uses the selected dependency version for cache/release identity, and prevents patch builds from publishing or saving base caches/bundles.

Review details

• Files reviewed: 5/5 changed files
• Comments generated: 1
• Review effort level: Lite

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