refactor(logging): flush the buffered logger directly from sockets

[EhabY]

Simplifies how sockets flush the connection log buffer.

The onConnectionFailure callback was threaded from the container through CoderApi.create into every ReconnectingWebSocket, even though the logger it flushed was already passed along the same path.

• Add a BufferedLogger interface (Logger plus flush) in logger.ts, replacing ConnectionLogBuffer.
• ReconnectingWebSocket and CoderApi take a BufferedLogger, and the socket calls flush directly on a terminal failure and once per unreachable outage.
• getLogger() returns the BufferedLogger, so getConnectionLogBuffer() is removed.
• Remove the callback option, its no-op default, and BufferingLogger.onConnectionFailure.

No behavior change: the flushed <reason> <route> strings are identical.

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