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

lifetime_annotations/lifetime.cc

diff --git a/lifetime_annotations/lifetime.cc b/lifetime_annotations/lifetime.cc
index 1652215..f088461 100644
--- a/lifetime_annotations/lifetime.cc
+++ b/lifetime_annotations/lifetime.cc
@@ -6,7 +6,9 @@
 
 #include "third_party/absl/strings/str_cat.h"
 
-namespace devtools_rust {
+namespace clang {
+namespace tidy {
+namespace lifetimes {
 
 constexpr int INVALID_LIFETIME_ID_EMPTY = 0;
 constexpr int INVALID_LIFETIME_ID_TOMBSTONE = 1;
@@ -79,4 +81,6 @@
   return os << lifetime.DebugString();
 }
 
-}  // namespace devtools_rust
+}  // namespace lifetimes
+}  // namespace tidy
+}  // namespace clang