chore(labs): improve build and test speed

This changeset optimizes the Guava build significantly by enabling
parallel build and test features supported by Maven. With these
flags enabled, only a few tests exhibit flaky behavior; applying a
sensible count of test retries (3) solves the problem.

As a result, the testsuite can now be executed often, because it
takes about 2 minutes to run. Building is also much faster. After
benchmarking different configurations, 2-threads-per-core and
2-test-forks-per-core seems optimal:

```
[INFO] Guava Maven Parent ..................... SUCCESS [  0.121 s]
[INFO] Guava: Google Core Libraries for Java .. SUCCESS [  9.681 s]
[INFO] Guava BOM .............................. SUCCESS [  0.120 s]
[INFO] Guava Testing Library .................. SUCCESS [ 47.883 s]
[INFO] Guava Unit Tests ....................... SUCCESS [01:57 min]  <--
[INFO] Guava GWT compatible libs .............. SUCCESS [  6.909 s]
```

When built and executed serially:
```
[INFO] Guava Maven Parent ..................... SUCCESS [  0.129 s]
[INFO] Guava: Google Core Libraries for Java .. SUCCESS [ 15.653 s]
[INFO] Guava BOM .............................. SUCCESS [  0.064 s]
[INFO] Guava Testing Library .................. SUCCESS [01:26 min]
[INFO] Guava Unit Tests ....................... SUCCESS [06:26 min] <--
[INFO] Guava GWT compatible libs .............. SUCCESS [ 11.092 s]
```

Benchmark hardware:
- Apple M2 Max, 96GB RAM
- macOS Sonoma 14.3.1
- GraalVM CE JVM 21.0.2

```
openjdk version "21.0.2" 2024-01-16
OpenJDK Runtime Environment GraalVM CE 21.0.2+13.1 (build 21.0.2+13-jvmci-23.1-b30)
OpenJDK 64-Bit Server VM GraalVM CE 21.0.2+13.1 (build 21.0.2+13-jvmci-23.1-b30, mixed mode, sharing)
```

- chore: enable parallel build
- chore: enable parallel test execution
- chore: enable parallel gc for maven
- chore: tune tiered compilation for maven
- chore: tune thread count for maven
- fix: enable test retries (max = 3) for parallel-flaky tests

Signed-off-by: Sam Gammon <sam@elide.ventures>

.mvn/jvm.config

@@ -0,0 +1 @@
+-XX:-TieredCompilation -XX:TieredStopAtLevel=1 -XX:+UseParallelGC -Djava.awt.headless=true

.mvn/maven.config

@@ -0,0 +1,2 @@
+-T2C
+--strict-checksums

pom.xml

@@ -12,6 +12,10 @@
   <description>Parent for guava artifacts</description>
   <url>https://github.com/google/guava</url>
   <properties>
+    <!-- Enable parallel test execution -->
+    <parallel>all</parallel>
+    <perCoreThreadCount>false</perCoreThreadCount>
+    <threadCount>48</threadCount>
     <!-- Override this with -Dtest.include="**/SomeTest.java" on the CLI -->
     <test.include>%regex[.*.class]</test.include>
     <truth.version>1.4.2</truth.version>
@@ -31,6 +35,7 @@
     <otherVariant.version>HEAD-android-SNAPSHOT</otherVariant.version>
     <otherVariant.jvmEnvironment>android</otherVariant.jvmEnvironment>
     <otherVariant.jvmEnvironmentVariantName>android</otherVariant.jvmEnvironmentVariantName>
+    <surefire.rerunFailingTestsCount>3</surefire.rerunFailingTestsCount>
   </properties>
   <issueManagement>
     <system>GitHub Issues</system>
@@ -230,7 +235,7 @@
         </plugin>
         <plugin>
           <artifactId>maven-surefire-plugin</artifactId>
-          <version>2.7.2</version>
+          <version>3.2.5</version>
           <configuration>
             <includes>
               <include>${test.include}</include>
@@ -249,6 +254,8 @@
             <!-- Set max heap for tests. -->
             <!-- Catch dependencies on the default locale by setting it to hi-IN. -->
             <argLine>-Xmx1536M -Duser.language=hi -Duser.country=IN ${test.add.opens}</argLine>
+            <reuseForks>true</reuseForks>
+            <forkCount>2C</forkCount>
           </configuration>
         </plugin>
         <plugin>