⚡ perf: Set cargo default to 24 threads for all builds

Created .cargo/config.toml with:
- jobs = 24 (all cargo builds use 24 threads by default)
- CARGO_INCREMENTAL = 1 (enable incremental compilation)

This affects all cargo commands in the project, making explicit -j 24
unnecessary in build scripts (though keeping them for clarity is fine).

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

.cargo/config.toml

@@ -0,0 +1,9 @@
+# Cargo configuration for Nyash project
+
+[build]
+# Use 24 threads by default for all cargo builds
+jobs = 24
+
+[env]
+# Environment variables for all cargo commands
+CARGO_INCREMENTAL = "1"