examples/rust: Rename hello_rust to rust/baremetal

Summary:
- Renamed hello_rust example to rust/baremetal to better reflect its purpose
- Updated file headers and Makefile paths
- Maintained all existing Kconfig options and functionality
- Prepares for future Rust development patterns where Cargo will be the
mainstream approach, with baremetal demonstrating traditional build method
- Creates clearer structure for Rust examples as we expand Rust support

Impact:
- No functional changes to the example itself
- Better organization of Rust examples under examples/rust/
- Existing configurations using this example will continue to work
- Build system will now look for the example in the new location

Testing:
- Confirmed Kconfig options remain unchanged
- GitHub CI passed and local build tested

Signed-off-by: Huang Qi <huangqi3@xiaomi.com>

examples/rust/baremetal/Kconfig

@@ -7,7 +7,8 @@ config EXAMPLES_HELLO_RUST
 	tristate "\"Hello, Rust!\" example"
 	default n
 	---help---
-		Enable the \"Hello, Rust!\" example
+		Enable the \"Hello, Rust!\" example to show how to build
+		and run a baremetal Rust application with rustc.
 
 if EXAMPLES_HELLO_RUST
 

examples/rust/baremetal/Make.defs

@@ -1,5 +1,5 @@
 ############################################################################
-# apps/examples/hello_rust/Make.defs
+# apps/examples/rust/baremetal/Make.defs
 #
 # SPDX-License-Identifier: Apache-2.0
 #
@@ -21,5 +21,5 @@
 ############################################################################
 
 ifneq ($(CONFIG_EXAMPLES_HELLO_RUST),)
-CONFIGURED_APPS += $(APPDIR)/examples/hello_rust
+CONFIGURED_APPS += $(APPDIR)/examples/rust/baremetal
 endif

examples/rust/baremetal/Makefile

@@ -1,5 +1,5 @@
 ############################################################################
-# apps/examples/hello_rust/Makefile
+# apps/examples/rust/baremetal/Makefile
 #
 # SPDX-License-Identifier: Apache-2.0
 #

examples/rust/baremetal/hello_rust_main.rs

@@ -1,5 +1,5 @@
 /****************************************************************************
- * apps/examples/hello_rust/hello_rust_main.rs
+ * apps/examples/rust/baremetal/hello_rust_main.rs
  *
  * SPDX-License-Identifier: Apache-2.0
  *