fix: make mvnw executable and raise javadoc heap for large beta SDK

- Set the executable bit on mvnw so Linux CI (GitHub Actions) can run it
  (was failing with exit 126 / Permission denied)
- Increase maven-javadoc-plugin fork heap to -J-Xmx4g; the beta SDK has
  27,817 source files and OOMed javadoc at 2g (Please increase memory)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: ramsessanchez

mvnw

@@ -182,7 +182,7 @@
                 <configuration>
                     <doclint>-missing</doclint>
                     <quiet>true</quiet>
-                    <additionalJOption>-J-Xmx2g</additionalJOption>
+                    <additionalJOption>-J-Xmx4g</additionalJOption>
                 </configuration>
             </plugin>