Fix the defects the rerunner removal uncovered

[hyperxpro]

Motivation:

Removing @RepeatedIfExceptionsTest (#2343) surfaced defects that were left out of that PR:

• The connection permit was returned only after the handler's onThrowable ran. A handler that re-submitted from there under maxConnections was refused with TooManyConnectionsException. NettyRequestThrottleTimeoutTest could not see it because its assertion was vacuous.
• An unreachable peer (NoRouteToHostException) was retried on NIO but not on native transports.
• A WebSocket send after close failed with a different exception depending on TLS timing, and isOpen() stayed true.
• When onRetry() threw, its exception replaced the real failure cause.
• Nothing stopped a connect failure from replaying a request that was already written.
• Several tests asserted nothing, slept, or shared static state. CI jobs had no timeout.

Modification:

• Release the permit in NettyRequestSender.abort before the handler is notified, through a new Channels.releasePermit. It is public only because the caller is in another package, and it is marked internal. A channel that gave its permit back is never pooled. HTTP/2 connections keep theirs.
• Close an aborted channel without waiting on the SslHandler's close_notify flush. HTTP/2 closes stay graceful.
• Treat NoRouteToHostException as a retryable connect failure on every transport.
• Add a write guard to the WebSocket pipeline that fails sends with ClosedChannelException once the peer's Close has been handled. A listener can still answer from onClose.
• retry() returns false when onRetry() throws, so the caller aborts with the real cause.
• NettyConnectListener.onFailure never replays once the request is written.
• Inject clocks into CombinedConnectionSemaphore and TimeoutsHolder through package-private constructors. The semaphore now times its budget with nanoTime.

Result:

A handler can re-submit from onThrowable without being refused, and failures report their real cause. WebSocket sends after close fail the same way on ws and wss