Prevent unnecessary rebuilds by adding rerun-if-changed directive

Add cargo:rerun-if-changed=build.rs to explicitly tell Cargo when to
rebuild. Without this directive, Cargo's default behavior is to rerun
the build script whenever any file in the package changes, causing
unnecessary rebuilds when this crate is used as a dependency.

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

Co-Authored-By: Claude <[email protected]>

Author: Nao-ris

build.rs

@@ -201,6 +201,7 @@ fn generate_bindings() -> Result<(), Box<dyn Error>> {
 }
 
 fn configure_rustc() -> Result<(), Box<dyn Error>> {
+    println!("cargo:rerun-if-changed=build.rs");
     println!("cargo:rerun-if-changed=src/wrapper.h");
     println!("cargo:rerun-if-changed={}", CBL_INCLUDE_DIR);
     println!("cargo:rerun-if-changed={}", CBL_LIB_DIR);