ci(ios): boot the simulator while the app builds

[datlechin]

Why

The iOS job left the simulator to xcodebuild test, which booted it only after the build. Recent runs waited 2 to 7 minutes between the end of the build and the first test.

Change

• Boot iPhone 18 Pro by UDID right after setup-xcode, so its first boot overlaps the build. The lookup takes the newest iOS runtime that has the device, as a destination by name does, and still downloads the platform when it is missing.
• xcodebuild test targets that UDID with -destination id=, so exactly one simulator boots. -parallel-testing-enabled NO stays.
• The iOS build turns the compilation cache off, as the macOS jobs do (every iOS log showed 0 hits).
• ci.md: iOS and Package Tests.

Verified

This PR's iOS run (39164087175) was the trial, and it regressed: 25.1 min against 13.2 to 16.7 without the early boot. The boot slowed setup-xcodegen plus download-libs.sh from 0.2 to 4.0 to 7.0 min. #3554 reverts the boot and keeps the cache off; its table has the step times.

[datlechin]

Trial result: both runs were about 8 minutes slower than the median (25.1 and 25.5 vs 17.2), since the boot starves the setup steps. #3554 puts the boot back after the build and keeps the cache-off line.