fix: support Windows host runtimes and stable native caching

[mertushka]

Purpose

Fix Windows native addon loading under compatible Node-API host runtimes and prevent stale vcpkg caches from rebuilding OpenSSL on every CI run.

Root cause

The addon linked delayed node.exe imports but omitted ${CMAKE_JS_SRC}. Under Bun on Windows, the first Node-API call could cross into a separately loaded Node runtime and crash the process. The standard cmake-js win_delay_load_hook.cc redirects those imports to the active host runtime.

Windows CI also cached vcpkg_installed under a key that ignored the MSVC toolset. GitHub Actions could restore an ABI-incompatible exact cache, vcpkg would remove and rebuild OpenSSL, and the immutable cache entry could not be replaced.

Changes

• Add ${CMAKE_JS_SRC} to the native addon target.
• Extend the native integration check to require the cmake-js delay-load hook.
• Rotate the Windows vcpkg cache namespace.
• Include the active MSVC toolset version in the cache key, falling back to the runner image version.

Impact

• Native/build impact: Windows addon linkage includes the standard cmake-js delay-load hook.
• CI impact: the first run populates a fresh toolset-specific vcpkg cache; later runs should reuse OpenSSL instead of rebuilding it.
• Public API impact: none.
• WPT/conformance impact: none; WebRTC semantics are unchanged.
• Browser impact: none.
• Bun impact: fixes the observed Windows native-addon load crash. This does not add a Bun support claim.

Validation

• npm run build
• npm run check
• npm run native:check
• npm test (52/52)
• Bun 1.3.14 Windows x64: package load and peer construction
• Bun 1.3.14 Windows x64: two-peer offer/answer, data-channel open, TSFN event delivery, string message exchange, and cleanup
• PowerShell MSVC toolset detection against Visual Studio Build Tools
• Composite action YAML parse
• git diff --check