Windows release builds were compiling and linking four release binaries
on a single runner, which slowed the release pipeline. The
Windows-specific logic also made `rust-release.yml` harder to read and
maintain.
## What Changed
- Extracted Windows release logic into a reusable workflow at
`.github/workflows/rust-release-windows.yml`.
- Updated `.github/workflows/rust-release.yml` to call the reusable
Windows workflow via `workflow_call`.
- Parallelized Windows binary builds with one 4-entry matrix over two
targets (`x86_64-pc-windows-msvc`, `aarch64-pc-windows-msvc`) and two
bundles (`primary`, `helpers`).
- Kept signing centralized per target by downloading both prebuilt
bundles and signing all four executables together.
- Preserved final release artifact behavior and filtered intermediate
`windows-binaries*` artifacts out of the published release asset set.
Michael Bolin