feat: support platform-specific SHA256 verification

[albertocavalcante]

Adds support for platform-specific BAZELISK_VERIFY_SHA256 variables, enabling SHA256 verification in multiplatform projects.

Fixes #522

Problem

The current BAZELISK_VERIFY_SHA256 only accepts a single hash value, but Bazel binaries have different SHA256 hashes per platform. Projects building on multiple platforms cannot use SHA256 verification.

Solution

Since each platform has a different binary with a different hash, Bazelisk now supports platform-specific hash variables:

• BAZELISK_VERIFY_SHA256_<OS>_<ARCH> - hash for a specific platform (e.g., BAZELISK_VERIFY_SHA256_LINUX_X86_64)
• BAZELISK_VERIFY_SHA256_NOJDK_<OS>_<ARCH> - hash for nojdk builds (when BAZELISK_NOJDK is enabled)
• BAZELISK_VERIFY_SHA256 - fallback used when no platform-specific hash is set

Supported Platforms

OS	Architectures
DARWIN	ARM64, X86_64
LINUX	ARM64, X86_64
WINDOWS	ARM64, X86_64

Example .bazeliskrc

BAZELISK_VERIFY_SHA256_DARWIN_ARM64=2c3cce548a4b6a97a2a5267712187b784b52714c4a2b0613e7386b15669d783c
BAZELISK_VERIFY_SHA256_DARWIN_X86_64=aa7e5fc364eaaba7f4f271dbf8c14172a5433f663cca6b130325df4b6569b3f0
BAZELISK_VERIFY_SHA256_LINUX_X86_64=c44a93f25398c68f904fa1d19b61d321de6c0d2f09dca375d7bc0dc9b9428403
BAZELISK_VERIFY_SHA256_LINUX_ARM64=cab23c59d3d39c5e5382f12cd116b47445afdff9813516c18ae3ee8836b3037f
BAZELISK_VERIFY_SHA256_WINDOWS_X86_64=463faee497df2913854d80776784137cb47f42960b4ef4e4f85068c8da4849a8
BAZELISK_VERIFY_SHA256_WINDOWS_ARM64=ab3db0b1f129436180927baa0f1f38e6d86a88fc9ee802572a76c9519a06f550

Implementation Notes

• Refactored downloadBazelIfNecessary to compute platform info once upfront
• Added FormatBazelFilename helper in platforms package
• Hash normalized to lowercase once at return (SHA256 hex is case-insensitive)
• Full backward compatibility with existing BAZELISK_VERIFY_SHA256

Test Plan

• Unit tests for getExpectedSHA256 (7 focused tests)
• Unit tests for FormatBazelFilename (2 tests)
• Shell integration test with Bazel 9.0.0 (all 6 platform/arch combinations)
• All existing tests pass

[fweikert]

Nit: can you please enumerate all valid values here? There might be some confusion regarding darwin vs macos or arm64 vs aarch64.

[albertocavalcante]

Absolutely! And agreed. Thanks for the feedback and review Florian. I should resume working in this during the weekend.

[fweikert]

Thank you for the feature (and the tests)!

[valco1994]

@albertocavalcante Do you need any help with this feature? From what I can see, you've already done most of the work.

[albertocavalcante]

@valco1994, thank you for offering assistance. I really appreciate it. To be honest, I had some issues with GitHub recently, and as a side effect, I ended up forgetting to finish it. I'll resume and finish it today or this weekend; otherwise, I will let you know.

Apologies.

[valco1994]

Wounderful, thank you for your work!