build(ci): adopt Windows 2025 runners #63

Why

The Windows verification jobs and release-proposal job still select the windows-2022 hosted image.
PR #62 proposes moving those existing jobs to windows-2025.
The update needs to preserve the native compatibility checks and the release-proposal boundary.
Related maintenance: #56.

Expected behavior

The existing Rust matrix, i686 execution, public API, package, and release-proposal jobs select windows-2025.
Keep the existing toolchains, target matrices, commands, permissions, path selection, required results, and artifact paths.
The separate protected release workflow retains its signing and publication boundaries.

Scope

Change only the five existing runner labels in .github/workflows/ci.yml and .github/workflows/release-plz.yml.
Preserve library behavior, the public API, dependency versions, and generated artifacts.

Validation

Confirm that the final diff contains exactly the five runner-label replacements and no other workflow change.
Run the applicable local workflow checks and the normal Windows project gate.
Verify the final head's native Rust matrix, i686 execution, ARM64 execution, public API, package checks, dependency review, selected code analysis, required summary, and release-age status.
Distinguish skipped and hosted-only checks from executed checks.
Resolve supported current-head review findings before acceptance.