[sdk] Treat Java SDK compiler warnings as build errors

[iwahbe]

Summary

Configures the Java SDK Gradle build to treat compiler warnings as errors (-Xlint:all -Werror on all JavaCompile tasks) and addresses every pre-existing warning so CI compiles cleanly.

Build configuration change

• tasks.withType(JavaCompile).configureEach { options.compilerArgs.addAll(['-Xlint:all', '-Werror']) } — applies to both main and test compilation.
• Excludes the proto-generated codegen package from javadoc, matching the existing pulumirpc exclusion.

Source changes

Resolves the warnings that -Werror then surfaces:

• serial: add private static final long serialVersionUID = 1L to ~14 exception classes (e.g. RunException, ResourceException, automation exceptions, KeyMissingException, nested InvokeException/CallException/etc.).
• varargs: add @SuppressWarnings(\"varargs\") alongside @SafeVarargs on methods like Output.all, Output.ofList, ResourceOptions.Builder.aliases. JDK 11's @SafeVarargs only suppresses the declaration-site warning; the call-site use of the non-reifiable array needs the additional suppression.
• try: add @SuppressWarnings(\"try\") to AutoCloseable classes/methods whose close() may throw InterruptedException (Workspace, WorkspaceStack, EventLogWatcher, LocalWorkspace, LocalPulumiCommand) and to ContextAwareCompletableFuture and Instrumentation which deliberately use try-with-resources for context-scoped side effects.
• rawtypes: parameterize new CompletableFuture<?>[0], new OutputInternal<>(...), etc. in CompletableFutures, DeploymentImpl, PropertyValueSerializer.
• cast: drop the redundant casts in PropertyValueSerializer and PropertyValueSerializerTest.
• unchecked: add line-scoped @SuppressWarnings(\"unchecked\") via local-variable declarations on each genuinely unavoidable type-erasure cast (e.g. inside Converter, Serializer, Deserializer, OutputData, the ImportMetadata/ExportMetadata reflection paths, Output.ensureOutput, Left/Right.flatMap, TypeShape.getType, MockMonitor.serializeToMap). Class-level suppression only used in the one case where the entire Builder pattern is (B) this (ResourceOptions.Builder — 21 identical casts).

No public method signatures change — only method bodies, locals, and annotations.

Test plan

• gradle assemble — passes (was the failure case before).
• gradle build — passes with 0 javac warnings.
• gradle testAll — passes locally.
• CI `prerequisites` (`gradle assemble`) passes.
• CI `java-sdk-tests` compile passes; the remaining failure (`LocalWorkspaceTest.testStateDeleteForce` timeout) reproduces on `main` and is unrelated to this PR.