Block on TLS auth in NetworkHandler

[kevin-montrose]

Follow up on #1714 - block in NetworkHandler.Start() methods on TLS auth.

TODO:

• dev targeting version ([DEV] Block on TLS auth in NetworkHandler #1750)

[Copilot]

Pull request overview

This PR follows up on #1714 by making TLS authentication completion a synchronous guarantee in NetworkHandler.Start(...), so callers no longer need to spin-wait for SslStream authentication before using the connection.

Changes:

• Updated NetworkHandler.Start(...) (client/server TLS overloads) to synchronously wait for TLS authentication via AsyncUtils.BlockingWait(...).
• Removed IsAuthenticated(out Exception fault) / authFault and deleted client-side spin-wait loops that previously polled for TLS auth completion.
• Updated benchmark embedded server path to stop spinning on TLS auth.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
libs/common/Networking/NetworkHandler.cs	Makes sync Start(...) wait for TLS auth; removes IsAuthenticated/authFault; updates related XML docs.
libs/common/LightClient.cs	Removes TLS-auth spin loop after networkHandler.Start(...).
libs/client/GarnetClient.cs	Removes TLS-auth spin loop after networkHandler.Start(...).
libs/client/ClientSession/GarnetClientSession.cs	Removes TLS-auth spin loop after networkHandler.Start(...).
benchmark/BDN.benchmark/Embedded/GarnetServerEmbedded.cs	Removes TLS-auth spin loop after handler.Start(...).

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