Move lifetime_annotations to namespace clang::tidy::lifetimes.

We're planning to upstream this to Clang-Tidy eventually, and we're already
preparing for that.

PiperOrigin-RevId: 442730445
diff --git a/lifetime_annotations/pointee_type.cc b/lifetime_annotations/pointee_type.cc
index 3121014..f33d48b 100644
--- a/lifetime_annotations/pointee_type.cc
+++ b/lifetime_annotations/pointee_type.cc
@@ -4,7 +4,9 @@
 
 #include "lifetime_annotations/pointee_type.h"
 
-namespace devtools_rust {
+namespace clang {
+namespace tidy {
+namespace lifetimes {
 
 clang::QualType PointeeType(clang::QualType type) {
   if (auto ptr_type = type->getAs<clang::PointerType>()) {
@@ -16,4 +18,6 @@
   return clang::QualType();
 }
 
-}  // namespace devtools_rust
+}  // namespace lifetimes
+}  // namespace tidy
+}  // namespace clang