fix: Avoid creating message string prematurely for streaming calls (#3622)

- Creating the string message prematurely puts a lot of strain on the JVM and GC, switch to the format version of `Preconditions.checkState` which only constructs the string if we throw the exception - Issue: #3621 Thank you for opening a Pull Request! Before submitting your PR, please read our [contributing guidelines](https://github.com/googleapis/gapic-generator-java/blob/main/CONTRIBUTING.md). There are a few things you can do to make sure it goes smoothly: - [x] Make sure to open an issue as a [bug/issue](https://github.com/googleapis/gapic-generator-java/issues/new/choose) before writing your code! That way we can discuss the change, evaluate designs, and agree on the general idea - [x] Ensure the tests and linter pass - [x] Code coverage does not decrease (if any source code was changed) - [x] Appropriate docs were updated (if necessary) Fixes #3621 ☕️

Author: mina-asham

gax-java/gax/src/main/java/com/google/api/gax/rpc/StateCheckingResponseObserver.java

@@ -43,7 +43,7 @@ public abstract class StateCheckingResponseObserver<V> implements ResponseObserv
  * ensuring consistent state.
  */
  public final void onStart(StreamController controller) {
- Preconditions.checkState(!isStarted, getClass() + " is already started.");
+ Preconditions.checkState(!isStarted, "%s is already started.", getClass());
  isStarted = true;
 
  onStartImpl(controller);
@@ -56,7 +56,7 @@ public final void onStart(StreamController controller) {
  * consistent state.
  */
  public final void onResponse(V response) {
- Preconditions.checkState(!isClosed, getClass() + " received a response after being closed.");
+ Preconditions.checkState(!isClosed, "%s received a response after being closed.", getClass());
  onResponseImpl(response);
  }
 
@@ -67,7 +67,7 @@ public final void onResponse(V response) {
  * state.
  */
  public final void onComplete() {
- Preconditions.checkState(!isClosed, getClass() + " tried to double close.");
+ Preconditions.checkState(!isClosed, "%s tried to double close.", getClass());
  isClosed = true;
  onCompleteImpl();
  }
@@ -79,7 +79,7 @@ public final void onComplete() {
  * consistent state.
  */
  public final void onError(Throwable t) {
- Preconditions.checkState(!isClosed, getClass() + " received error after being closed", t);
+ Preconditions.checkState(!isClosed, "%s received error after being closed", t, getClass());
  isClosed = true;
  onErrorImpl(t);
  }