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>

Cargo.toml

@@ -1,9 +1,9 @@
 [package]
 name = "btest-rs"
-version = "0.1.0"
+version = "0.3.0"
 edition = "2021"
-description = "MikroTik Bandwidth Test (btest) server and client — a Rust reimplementation"
-license = "MIT"
+description = "MikroTik Bandwidth Test (btest) server and client with EC-SRP5 auth — a Rust reimplementation"
+license = "MIT AND Apache-2.0"
 repository = "https://github.com/samm-git/btest-opensource"
 keywords = ["mikrotik", "bandwidth", "btest", "network", "benchmarking"]
 categories = ["command-line-utilities", "network-programming"]
@@ -27,6 +27,10 @@ tracing-subscriber = { version = "0.3", features = ["env-filter"] }
 rand = "0.8"
 socket2 = "0.5"
 anyhow = "1.0.102"
+num-bigint = "0.4.6"
+num-traits = "0.2.19"
+num-integer = "0.1.46"
+sha2 = "0.11.0"
 
 [profile.release]
 opt-level = 3