enable short backtraces by default

Uses panic_backtrace_config feature to set BacktraceStyle::Short,
so panics show useful backtraces without needing RUST_BACKTRACE=1.

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/bin/consciousness.rs

@@ -1,2 +1,7 @@
+#![feature(panic_backtrace_config)]
 #![warn(unreachable_pub)]
-fn main() { consciousness::user::main() }
+
+fn main() {
+    std::panic::set_backtrace_style(std::panic::BacktraceStyle::Short);
+    consciousness::user::main()
+}