Warn when skip doctor/skip checkup can't find any attached devices

[dfabulich]

Fixes #186

skip doctor warns if it can't find devices

If skip doctor doesn't detect any attached Android devices, it will log a warning, like this:

[!] No Android devices running. Xcode builds will fail until you attach a device, launch an emulator in Android Studio, or run: skip android emulator launch

Otherwise, it will log how many devices it detected:

[✓] Android devices: 1 connected

skip init can now install to an emulator

skip init has a new argument, --launch-android, which will attempt to launch the app on an emulator. I don't expect regular users will want to use it much, but I needed it for skip checkup

skip checkup will attempt to launch if it detects devices

When skip checkup runs the doctor command, it will return a boolean, saying whether it detected any devices. If it did detect devices, skip checkup will pass launchAndroid: true to initSkipProject. This will install and launch the app on an attached device.

If doctor detected no devices, checkup will pass launchAndroid: false. The conclusion will be successful with 1 warning.

Skip Pull Request Checklist:

• REQUIRED: I have signed the Contributor Agreement
• REQUIRED: I have tested my change locally with swift test
• OPTIONAL: I have tested my change on an iOS simulator or device
• OPTIONAL: I have tested my change on an Android emulator or device

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• AI was used to generate or assist with generating this PR. Please specify below how you used AI to help you, and what steps you have taken to manually verify the changes.

I mostly used Cursor to generate this code. I reviewed every line and tested it manually:

• skip doctor with/without a running emulator
• skip checkup with/without a running emulator
  • … and I verified that the app actually launched on the emulator

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