TB 41921: Do not wait for TorSettings to initialise before allowing a
bootstrap.

Instead, we wait for TorSettings as required: for preparing
AutoBootstrap attempts, and TorBootstrapRequest should already wait for
TorSettings before attempting to connect.

TB 41921: Ensure TorProviderBuilder.build can be called immediately
after TorProviderBuilder.init returns (without await).

We make sure that the `#provider` instance is created before any break
in execution caused by an `await`.

TB 41921: Do not wait for TorProviderBuilder.init since it is no longer
async.

TB 41921: Add a note to TorBootstrapRequest explaining the expectation
that the TorProvider has already read from TorSettings before it
connects.