fix: resolve TypeScript errors with moduleResolution nodenext and skipLibCheck false

[R-Delfino95]

Resolves #1299

• Vendor mux-embed's type declarations into playback-core/src/vendor/mux-embed.ts. TypeScript compiles this into dist/types/vendor/mux-embed.d.ts and emits a correct relative reference path for consumers.
• Added a vendor:types npm script (scripts/vendor-mux-embed-types.mjs) that copies the types directly from node_modules/mux-embed/dist/types/mux-embed.d.ts. It's hooked into prebuild:types so it runs automatically on every build — keeping the vendored copy in sync with whatever version of mux-embed is installed.
• Moved @types/google_interactive_media_ads_types to dependencies in mux-video.
• Removed the broken /// <reference path> from mux-video/src/ads/index.ts — it's no longer needed since playback-core's vendored reference propagates transitively.

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Note

Medium Risk
Medium risk because it changes how @mux/playback-core ships TypeScript declarations (new vendored mux-embed types and a pre-build generation step), which can affect downstream type resolution and builds.

Overview
Fixes NodeNext/skipLibCheck=false TypeScript build failures by vendoring mux-embed type declarations into @mux/playback-core and updating src/types.ts to reference the vendored file instead of node_modules.

Adds a vendor:types script (run automatically via prebuild:types) to copy mux-embed’s .d.ts into src/vendor, and ignores the generated vendor directory in ESLint/Prettier. Also adjusts packaging dependencies: moves @types/google_interactive_media_ads_types to mux-video runtime dependencies, removes an unneeded/broken triple-slash reference in mux-video ads entry, and tweaks a couple dependency version ranges in the lockfile.

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