Fix Starlark CPU profiler resource leaks in Main and BlazeCommandDispatcher

[SebTardif]

Problem

Two resource management bugs exist in the Starlark CPU profiling lifecycle:

1. Main.java (-cpuprofile flag)
The output stream is opened before checking whether profiling startup succeeded. stopCpuProfile() is called unconditionally even when startCpuProfile() returns false (native support unavailable), which can trigger a stop without start error. The output stream is also leaked on failure.

2. BlazeCommandDispatcher.java (--starlark_cpu_profile flag)
The output stream created for the profile is leaked on several early return paths:

• IllegalStateException from startCpuProfile() (e.g. SIGPROF in use)
• Early exit from option parsing errors or module beforeCommand failures
• Uncaught exceptions reaching the finally block

Additionally, if stopCpuProfile() throws IOException in the normal finalization path, the finally block could attempt a second stop, retriggering a stop without start error.

Fix

Main.java:

• Track whether startCpuProfile() actually succeeded
• Only call stopCpuProfile() when it did; otherwise close the output stream directly
• Wrap the logic in try/finally for proper cleanup
• Extract a package-local run() method so the logic is testable without System.exit()

BlazeCommandDispatcher.java:

• Track both the output stream and the profiling-started boolean as local variables
• Close the output stream on the startCpuProfile() exception path
• Add cleanup in the finally block: stop profiling if started, or close the stream if not
• Clear both tracking variables after successful stop to prevent double-stop on IOException
• Add a helper closeStarlarkCpuProfileOutput() for safe stream cleanup

Tests

• MainTest (src/test/java/net/starlark/java/cmd/MainTest.java): Verifies -cpuprofile does not fail when profiling is unsupported (native support set to null).
• BlazeCommandDispatcherTest: Two new methods:
  • starlarkCpuProfileOutputIsClosedWhenProfilingInitializationFails: Uses a fake native support where startTimer() returns false; verifies the output stream is closed and the correct failure code is returned.
  • starlarkCpuProfileOutputIsClosedOnEarlyReturnAfterStart: Uses a fake native support where startTimer() succeeds; triggers an early exit via --config=UNDEFINED_CONFIG_VALUE; verifies the output stream is closed.