Add EC-SRP5 authentication (RouterOS >= 6.43)

Client: auto-detects 03 response and performs EC-SRP5 handshake
Server: --ecsrp5 flag enables Curve25519 Weierstrass EC-SRP5 auth
  btest -s -a admin -p password --ecsrp5

Protocol: [len][payload] framing (no 0x06 handler, unlike Winbox)
Crypto: Curve25519 in Weierstrass form, SHA256, SRP key exchange

Based on MarginResearch/mikrotik_authentication (Apache 2.0).
Verified against MikroTik RouterOS 7.x via MITM protocol analysis.

34 tests (10 unit, 6 EC-SRP5 integration, 8 base integration, 10 doc-tests).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

LICENSE

@@ -3,7 +3,11 @@ MIT License
 Copyright (c) 2026 btest-rs contributors
 
 Based on btest-opensource by Alex Samorukov (https://github.com/samm-git/btest-opensource)
-Original work Copyright (c) 2016 Alex Samorukov
+Original work Copyright (c) 2016 Alex Samorukov (MIT License)
+
+EC-SRP5 authentication based on research by Margin Research
+(https://github.com/MarginResearch/mikrotik_authentication)
+Original work Copyright (c) 2022 Margin Research (Apache License 2.0)
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
@@ -22,3 +26,10 @@ AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
+
+---
+
+NOTICE: This project includes code derived from works under the Apache License 2.0.
+The EC-SRP5 elliptic curve implementation is based on MarginResearch/mikrotik_authentication.
+See https://github.com/MarginResearch/mikrotik_authentication/blob/master/LICENSE
+for the full Apache 2.0 license text.