Add Transport.isKeyExchangeRequired() to avoid unnecessary KEXINIT

[exceptionfactory]

This pull request addresses SSH_MSG_UNIMPLEMENTED errors during key exchange described in issue #810.

Changes include adding isKeyExchangeRequired() to the Transport interface, with an implementation in TransportImpl that checks the status of Key Exchange completion and processing.

Checking KeyExchanger.isKexDone() indicates that at least one key exchange has not been completed, and checking KeyExchanger.isKexOngoing() indicates that a key exchange is not in progress. Checking Transport.isKeyExchangeRequired() in SSHClient.onConnect() avoids sending an additional SSH_MSG_KEXINIT packet when a key exchange is already in progress or completed.

Additional changes include adding a started timestamp when setting a thread name in ThreadNameProvider. The started timestamp makes it easier to distinguished between threads for multiple connections to the same remote host and port.

[codecov-commenter]

Codecov Report

Merging #811 (7446307) into master (430cbfc) will decrease coverage by 0.02%.
The diff coverage is 57.14%.

@@             Coverage Diff              @@
##             master     #811      +/-   ##
============================================
- Coverage     64.71%   64.68%   -0.03%     
- Complexity     1459     1460       +1     
============================================
  Files           210      210              
  Lines          8519     8524       +5     
  Branches        778      779       +1     
============================================
+ Hits           5513     5514       +1     
- Misses         2601     2603       +2     
- Partials        405      407       +2     

Impacted Files	Coverage Δ
...java/net/schmizz/sshj/transport/TransportImpl.java	64.87% <0.00%> (-0.27%)	⬇️
src/main/java/net/schmizz/sshj/SSHClient.java	58.52% <50.00%> (-0.44%)	⬇️
...com/hierynomus/sshj/common/ThreadNameProvider.java	71.42% <100.00%> (+4.76%)	⬆️
...t/schmizz/sshj/connection/ConnectionException.java	33.33% <0.00%> (-11.12%)	⬇️
...zz/sshj/connection/channel/ChannelInputStream.java	77.27% <0.00%> (-3.04%)	⬇️
.../java/net/schmizz/sshj/transport/KeyExchanger.java	77.17% <0.00%> (+0.54%)	⬆️
.../main/java/net/schmizz/sshj/sftp/PacketReader.java	95.74% <0.00%> (+4.25%)	⬆️

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[hierynomus]

@exceptionfactory 1 test failed, can you have a look?

[exceptionfactory]

Thanks for the feedback @hierynomus!

The test succeeded on a local build, but it appears to be an intermittent timing issue where the KeepAlive Thread may not have started. I pushed a new commit that moves the TIMED_WAITING status assertion after attempting authentication, which should make the test more reliable.

[hierynomus]

Merged! Thanks for the improvement

[exceptionfactory]

Thank you very much @hierynomus! Are you planning to do a new release of SSHJ soon? This would be very helpful for downstream consumers, and the internal nature of the Transport changes make it difficult to patch around without upgrading.