fix: make vendored OpenSSL unix-only

Windows uses schannel via native-tls and doesn't need vendored
OpenSSL. Perl is not reliably available on Windows CI runners,
causing the vendored build to fail.

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

Author: jacderida

ant-core/Cargo.toml

@@ -34,7 +34,6 @@ futures = "0.3"
 postcard = { version = "1.1.3", features = ["use-std"] }
 rmp-serde = "1"
 hex = "0.4"
-openssl = { version = "0.10", features = ["vendored"] }
 tracing = "0.1"
 bytes = "1"
 lru = "0.16"
@@ -45,6 +44,7 @@ tracing-subscriber = { version = "0.3", features = ["env-filter"] }
 
 [target.'cfg(unix)'.dependencies]
 libc = "0.2"
+openssl = { version = "0.10", features = ["vendored"] }
 
 [target.'cfg(windows)'.dependencies]
 windows-sys = { version = "0.61", features = ["Win32_Foundation", "Win32_System_Console", "Win32_System_Threading"] }