feat: Publish game artifacts during the build, run only the executable for demo runs

[mujacica]

• Currently building/releasing the Demo game takes ~2 hours
• We needed a better way to execute the game quickly for the Demo/Sandbox
• Split the build into two parts: build + package + upload and download + run
• Use Github actions to manage files

[mujacica]

Build/Release: https://github.com/getsentry/unreal-tower/actions/runs/16779493517
Run: https://github.com/getsentry/unreal-tower/actions/runs/16796911660

Run was done in 3 minutes 14 seconds

[seer-by-sentry]

Potential bug: The `run-demo` workflow uses an incorrect path to find the packaged executable, failing to account for the `WindowsNoEditor` subdirectory created during the build process.

• Description: The Unreal Engine build process, using BuildCookRun with the -archive flag for the Win64 platform, packages the executable inside a WindowsNoEditor subdirectory. The run-demo.yml workflow downloads the build artifact but incorrectly attempts to find SentryTower.exe at the root of the downloaded directory. This path mismatch in the Join-Path command will cause the workflow to fail with a "file not found" error, preventing the demo from running.
• Suggested fix: Update the path construction in run-demo.yml to include the WindowsNoEditor subdirectory created by the Unreal Engine build process. Change Join-Path $downloadPath "SentryTower.exe" to Join-Path $downloadPath "WindowsNoEditor" "SentryTower.exe".
  _{severity: 0.85, confidence: 0.98}

_{Did we get this right? 👍 / 👎 to inform future reviews.}