Feat/sha256 libra

[jackieismpc]

Summary

#72
This PR introduces initial SHA-256 support for the core commands. The goal is to make it possible to run the existing command set with SHA-256 object IDs, while keeping the current SHA-1 behavior intact and configurable.

Changes

• Added SHA-256 support to the core command layer so that object IDs can be computed and interpreted using either SHA-1 or SHA-256.
• Introduced helper functions at the top-level entry points to:
  • Resolve the selected hash algorithm (e.g. from config/CLI/environment).
  • Initialize the global hash kind once during startup.
  • Expose a unified abstraction so downstream code no longer needs to care whether SHA-1 or SHA-256 is used.
• Refactored existing call sites to rely on the new initialization helpers instead of hard-coded SHA-1 usage.

Behavior and Compatibility

• Default behavior remains unchanged for existing users (SHA-1 by default), unless SHA-256 is explicitly selected.
• The new initialization helpers are designed to be reusable, so future hash algorithms (or additional SHA-256-related features) can be integrated with minimal changes to the call sites.

[Copilot]

Pull request overview

This PR introduces initial SHA-256 support to the Libra Git engine core command layer, enabling the use of SHA-256 object IDs alongside the existing SHA-1 implementation. The changes are substantial and well-structured:

Purpose: Enable SHA-256 as an alternative hash algorithm for Git object IDs while maintaining backward compatibility with SHA-1 as the default.

Key Changes:

• Replaced the concrete SHA1 type with an abstract ObjectHash type throughout the codebase
• Added hash algorithm selection during repository initialization (--object-format sha1|sha256)
• Introduced global hash kind management and initialization helpers
• Updated all commands, storage, and utility functions to work with the abstract hash type
• Added comprehensive test coverage for SHA-256 workflows

Reviewed changes

Copilot reviewed 144 out of 145 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
third-party/rust/crates/**/BUCK	Cleanup of unused third-party dependency definitions and feature flags
tests/command/*.rs	Added SHA-256 test cases for core workflows (commit, cherry-pick, checkout, blame, reset)
src/utils/*.rs	Updated utility functions to use ObjectHash abstraction
src/internal/*.rs	Updated internal types (Branch, Head, Tag, Reflog) to use ObjectHash
src/command/*.rs	All commands updated to support both hash algorithms with proper validation
src/command/init.rs	Enhanced to accept and validate --object-format parameter, initialize global hash kind
src/command/index_pack.rs	Added hash kind validation for pack index operations
src/command/commit.rs	Removed hard-coded empty tree hash, made it dynamic based on hash kind