Release 0.5.0

[vik-borisov]

Summary

• Bump package version to 0.5.0 and update git2dart_binaries to >=1.11.0 <1.12.0.
• Add public APIs for commit graph, ignore, message, pathspec, and additional helpers across config, diff, oid, repository, and tree.
• Add Flutter iOS platform support with shared PlatformSpecific.initialize().
• Refresh public API documentation for consistency.