Prevent repeater from adding itself to flood path multiple times

[andrewdefilippis]

Summary

• When a repeater goes rogue, it can inject its own id into the path multiple times.
• Before appending this node's hash to the path in routeRecvPacket(), check if the last 2 path entries already match — if so, drop the packet instead of retransmitting
• Allows up to 2 consecutive identical hashes (legitimate collision) but blocks 3+ (loop indicator)

Test plan

• Verify build compiles cleanly (confirmed with PlatformIO Heltec_v3_repeater)
• Trace attack scenario: packet with path [... 20 20] arriving at repeater with hash 0x20 is correctly dropped
• Verify normal forwarding: packet with path [... AB] at repeater 0x20 forwards as [... AB 20]
• Verify single collision: packet with path [... 20] at repeater 0x20 forwards as [... 20 20]

🤖 Generated with Claude Code

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Description updated by myself to clarify the underlying issue as a rogue repeater injecting itself into the path multiple times, nearly exhausting max path, and transmitting corrupted messages.

example:

05 16 56 AB 86 7E 75 20 20 20 20 20 20 20 20 20 75 07 24 BE 53 A5 2D 6B 7C 9E 06 CD 97 A3 AD C0 FC 68 41 AC

https://discord.com/channels/1343693475589263471/1391673743453192242/1474609553533440020

[andrewdefilippis]

As a quick note, this change would be better aligned with 2-byte repeater ids to have a more protected mesh. It can also be improved by allowing all repeaters to detect 3+ consecutive ids (which should be highly unlikely), and drop the packet.