fix(doctest): use platform-specific temp paths in command module examples

The doctest for the command module was using hardcoded /tmp path which doesn't
exist on Windows, causing the doctest to fail when running on Windows CI runners.
Fixed by using cfg!(windows) to select appropriate temp directory path on each platform.

Fixes Windows doctest failure: crates/mcp-core/src/command.rs - command (line 16)

All 352 tests passing.

Author: bug-ops

crates/mcp-core/src/command.rs

@@ -17,16 +17,21 @@
 //! use mcp_core::validate_command;
 //!
 //! // Valid absolute path
-//! # std::fs::write("/tmp/test-mcp-server", "#!/bin/sh\n").unwrap();
+//! # let temp_file = if cfg!(windows) {
+//! #     std::env::temp_dir().join("test-mcp-server.exe")
+//! # } else {
+//! #     std::path::PathBuf::from("/tmp/test-mcp-server")
+//! # };
+//! # std::fs::write(&temp_file, "#!/bin/sh\n").unwrap();
 //! # #[cfg(unix)]
 //! # {
 //! # use std::os::unix::fs::PermissionsExt;
-//! # let mut perms = std::fs::metadata("/tmp/test-mcp-server").unwrap().permissions();
+//! # let mut perms = std::fs::metadata(&temp_file).unwrap().permissions();
 //! # perms.set_mode(0o755);
-//! # std::fs::set_permissions("/tmp/test-mcp-server", perms).unwrap();
+//! # std::fs::set_permissions(&temp_file, perms).unwrap();
 //! # }
-//! let result = validate_command("/tmp/test-mcp-server");
-//! # std::fs::remove_file("/tmp/test-mcp-server").ok();
+//! let result = validate_command(temp_file.to_str().unwrap());
+//! # std::fs::remove_file(&temp_file).ok();
 //! # if result.is_err() {
 //! #     // On some systems, execution permission check might fail
 //! #     return;