Add RAR to I2NP DSM
WIP

so it doesn't null out the contained message.
Required for SSU2.
Unrelated TunnelDispatcher cleanup done while trying to find the problem.

- Don't require AES keys for short records
- Derive keys from noise ck
- Use derived keys to garlic-encrypt reply at OBEP
- Register reply key with SKM
- Only use short message for client tunnels if client supports EC
- Set nonce for chacha/poly reply record
- Add tagsReceived() for single tag to MuxedSKM
- Add extended TunnelCreatorConfig.toStringFull()
- BRR toString() enhancements
- Test enhancements

- remove ITBM
- remove plaintext slot from OTBRM

- Remove ITBM, change record length from 236 to 218 bytes
- Fix check of blank record in BuildReplyHandler
- Fix offset constants for short record in BuildRequestRecord
- Fix BuildMessageTestStandalone test 6 (short inbound)
- ITBM class removal TODO

- Add new internal-only ShortTunnelBuildReplyMessage,
  for processing of STBM as a reply.
- Add support for inbound tunnel tests to TunnelBuildMessageStandalone.
  The ITBM test is WIP.
- Add checks for unset plaintext record in ITBM and OTBRM

WIP, still disabled, proposal not complete

- Use ChaCha20 to encrypt/decrypt records
- Add OTBRM methods for plaintext record
- Add OTBRM checks for correct plaintext slot number
- Add BRR checks to prevent use of nonexistent AES key/IV
- Set plaintext reply at OBEP in BuildHandler
- Allow OTBRM in InboundMessageDistributor
- Remove timing measurements in BuildMessageProcessor.decrypt()
- Add test to BuildMessageTestStandalone for outbound build
- Add check for all replies to BuildMessageTestStandalone
- Log tweaks

- Generate and parse short record format
- Encrypt and decrypt short records
- Register handlers for 3 new messages ITBM/STBM/OTBRM
- Send ITBM/STBM if all hops support it (disabled)
- Reply with OTBRM at OBEP if STBM received (disabled)
- Send STBM at IBGW if ITBM received (disabled)
- Add logic for when to send new messages
- ChaCha encryption of other short records
- Fix compare logic in ITBM parser (ticket #2814)

All is still preliminary, disabled, untested; proposal is still incomplete

Still todo:
- Fill in plaintext record for ITBM/OTBRM
- OTBRM key/tag

Rename ShortTunnelBuildReplyMessage to OutboundTunnelBuildReplyMessage (type 26)
Add InboundTunnelBuildMessage (type 27)
Add methods for plaintext record
Update readMessage() and writeMessageBody()
Fix calculateWrittenLength()
Update javadocs
WIP, untested, not hooked in yet

WIP - not hooked in yet

Extend lookup expire time
Cleanups

- Change router ECIES SKM to use N pattern, remove Elligator2, to match proposal changes
- Allow encrypted messages to ECIES routers
- Allow ECIES routers to become floodfill
- Add XDH factory to VM comm system for tests

The #ls2 team plans to change the specification and re-enable after the 0.9.48 release

Fixup test as required

Additional checks on ECIES BRR to catch old/buggy routers
Detailed logging of ECIES BRR decrypt fails

Preliminary, proposal not finalized, subject to change
Not yet compatibility tested with other implementations
Add peers to match requested length for explicitPeers
remove commented out code
log tweaks

Tag.toBase64() optimization
Javadoc fixes

Pass CloveSet to/from ECIESEngine

Improve DataMessage.toString()

I2CP: Don't require privkeys for meta in CLS2 message