[build_manager] Raise exception on disk exhaustion instead of fatal exit

[PauloVLB]

Context

When build setup fails to make disk space, calling log_fatal_and_exit (which calls sys.exit()) silently crashes the bot in the middle of utask_main. This prevents task post-processing or proper debugging in the uworker model.

For more details, see b/506045195.

Solution

• Replaced the fatal log_fatal_and_exit calls with logs.error logging and a custom BuildManagerError exception in _download_and_open_build_archive and _unpack_build.
• Updated CustomBuild._unpack_custom_build to return False on disk exhaustion, aligning its behavior with RegularBuild.

This allows tasks encountering disk exhaustion to fail gracefully, complete their post-processing (reporting the build setup failure back to the coordinator), and allow the bot to continue running subsequent tasks without a process restart.

---

Verification & Testing Logs

The following logs from a local test run illustrate the new execution flow:

1. The first task runs, encounters simulated disk exhaustion, logs the error, raises the exception, and fails gracefully to reach postprocess.
2. The second task runs on the same bot immediately afterwards, successfully allocates space, and finishes successfully.

INFO:run_bot:>>> STARTING RUN 1: Executing task with FAILING _make_space mock <<<
INFO:run_bot:Starting utask_preprocess...
INFO:run_bot:Picked fuzz target webnn_graph_impl_fuzzer_WebNNGraphImplFuzzer_NPU_SingleOpLstm_fuzzer for fuzzing.
INFO:run_bot:Starting utask_main...
...
INFO:run_bot:Opening an archive over HTTP, skipping archive download.
ERROR:run_bot:Failed to make space for build. Cleared all data directories to free up space.
ERROR:run_bot:Unable to unpack build archive gs://chromium-browser-libfuzzer/linux-release-asan-schema-v1/libfuzzer-schema-v1-linux-release-1628559.zip: Failed to make space for build.
Traceback (most recent call last):
  File "src/clusterfuzz/_internal/build_management/build_manager.py", line 584, in _unpack_build
    raise BuildManagerError('Failed to make space for build.')
clusterfuzz._internal.build_management.build_manager.BuildManagerError: Failed to make space for build.
ERROR:run_bot:Failed to set up a build.
INFO:run_bot:Starting postprocess on trusted worker.
INFO:run_bot:Utask local: done.

INFO:run_bot:>>> RESTORED ORIGINAL build_manager._make_space BEHAVIOR <<<
INFO:run_bot:>>> STARTING RUN 2: Executing task with ORIGINAL DEFAULT _make_space behavior <<<
INFO:run_bot:Starting utask_preprocess...
INFO:run_bot:Picked fuzz target services_unittests_StructTraitsTest_BeginFrameAckFuzz_fuzzer for fuzzing.
...
INFO:run_bot:Build took 0.01 minutes to unpack.
INFO:run_bot:Retrieved build r1628559.
INFO:run_bot:Fuzzing round 0.
...
INFO:run_bot:All fuzzing rounds complete.
INFO:run_bot:Utask local: done.

As this error is difficult to safely reproduce in dev environments, we are deploying this change directly to production and will monitor bot metrics.