feat: add run() and binary entry points for all servers and init

Every server now has lib.rs (testable) + main.rs (deployable binary).
Binary is 3 lines: extern crate userspace_rt + call run().
Hardware servers use feature flags for adapter selection.
9 RISC-V binaries ready for the disk image.

crates/servers/log-server/src/lib.rs

@@ -6,3 +6,9 @@ pub mod server;
 #[cfg(test)]
 #[path = "tests/mod.rs"]
 mod tests;
+
+pub fn run() -> ! {
+    let mut srv = server::LogServer::new();
+    server_framework::serve(&mut srv, 0);
+    loop { userspace::syscall::yield_now(); }
+}

crates/servers/log-server/src/main.rs

@@ -0,0 +1,9 @@
+#![no_std]
+#![no_main]
+
+extern crate userspace_rt;
+
+#[unsafe(no_mangle)]
+extern "C" fn main() {
+    log_server::run();
+}