- Update version info for the `1.0.0-preview.4` release.
- Use deploy box and `GitHubRelease` task to create the GitHub draft release.
- Make sure the `Runspace` is available when importing the `AIShell` module and throw otherwise.
  - When validating packages, I found there were rare cases where the `Runspace` instance passed to the constructor of `AIShell.Integration.Channel` is `null`. The constructor is used only in the public static method `CreateSingleton` which is called from `AIShell.psm1` to create a singleton of the `Channel` type upon importing the `AIShell` module.
  - In `AIShell.psm1`, we call `CreateSingleton` with `$host.Runspace` to pass in the `Runspace` instance, and the module's manifest defines `PowerShellHostName = 'ConsoleHost'`, so in theory, `$host.Runspace` should never be null, but that just happened.
  - I'm guessing it could be related to the `CompletionPredictor` module loaded from my profile, which attempts to sync with the modules loaded in the default session from a separate `Runspace` -- somehow, the `Channel` singleton got created from that separate `Runspace` instead of the default session -- but I cannot prove it.
  - To address this issue, I added restricted checks in both `AIShell.psm1` and the constructor of `Channel` type, to make sure that a `Channel` singleton can be created only if the `Runspace` instance is available. Related changes are in this commit: a447dee.

…ded (#381)

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