Move StaticLifetime/Singleton into datadog.perfcontract and meta-annotate with @PerfContract

Relocates both annotations out of the legacy datadog.trace.api.function
package into the new datadog.perfcontract package (introduced by #12647),
alongside PerfContract/SuppressPerfContract, and adds @PerfContract so
tooling can discover them as perf-contract markers the same way it
already discovers Strategy/StrategyConsumer/NoEscape. No other code
references either annotation, so no import-site updates are needed.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: dougqh

…atadog/trace/api/function/Singleton.java …java/datadog/perfcontract/Singleton.javainternal-api/src/main/java/datadog/trace/api/function/Singleton.java renamed to internal-api/src/main/java/datadog/perfcontract/Singleton.java internal-api/src/main/java/datadog/trace/api/function/Singleton.java renamed to internal-api/src/main/java/datadog/perfcontract/Singleton.java

@@ -1,4 +1,4 @@
-package datadog.trace.api.function;
+package datadog.perfcontract;
 
 import java.lang.annotation.Documented;
 import java.lang.annotation.ElementType;
@@ -21,8 +21,8 @@
  * <p>This is a documentation-and-tooling marker; it changes no behavior.
  *
  * <p><b>v1 posture: trusted declaration, not independently verified.</b> This is the same stance
- * the other perf-contract annotations take toward {@code static final} itself -- declared, not
- * proven. Verifying it for real (a single construction site, or an instance reachable only via one
+ * the other perf-contract markers take toward {@code static final} itself -- declared, not proven.
+ * Verifying it for real (a single construction site, or an instance reachable only via one
  * static/DI-registered path) is a call-site/construction-graph problem, out of scope for v1.
  * Annotating a class that is, in fact, constructed more than once defeats every guarantee
  * downstream checks (starting with {@link StaticLifetime}) build on top of this annotation -- apply
@@ -39,6 +39,7 @@
  * annotation. See {@link StaticLifetime}'s own Checker contract section for the full rule.
  */
 @Documented
+@PerfContract
 @Retention(RetentionPolicy.CLASS)
 @Target(ElementType.TYPE)
 public @interface Singleton {}

…g/trace/api/function/StaticLifetime.java …datadog/perfcontract/StaticLifetime.javainternal-api/src/main/java/datadog/trace/api/function/StaticLifetime.java renamed to internal-api/src/main/java/datadog/perfcontract/StaticLifetime.java internal-api/src/main/java/datadog/trace/api/function/StaticLifetime.java renamed to internal-api/src/main/java/datadog/perfcontract/StaticLifetime.java

@@ -1,4 +1,4 @@
-package datadog.trace.api.function;
+package datadog.perfcontract;
 
 import java.lang.annotation.Documented;
 import java.lang.annotation.ElementType;
@@ -25,7 +25,7 @@
  * object, instead of once as a {@code static} field -- so the cache was allocated and thrown away
  * on every request and never actually amortized anything. It compiled, ran, and passed tests while
  * quietly defeating the entire point of caching -- the same silent-failure shape as the other
- * perf-contract annotations in this package.
+ * perf-contract markers.
  *
  * <p>This is a documentation-and-tooling marker; it changes no behavior. It exists to telegraph the
  * constraint to readers and to give a future checker something to verify. The discipline it names
@@ -78,6 +78,7 @@
  * </ul>
  */
 @Documented
+@PerfContract
 @Retention(RetentionPolicy.CLASS)
 @Target(ElementType.FIELD)
 public @interface StaticLifetime {}