[Corpus] Refactor and add wildcard support for feature flag

[PauloVLB]

Problem

The previous feature flag implementation for enabling threaded storage operations was somewhat rigid and required explicitly listing every single fuzz target. This made it difficult to scale the solution or enable it globally for specific deployments (like OSS-Fuzz) without maintaining huge lists. Additionally, the matching was case-sensitive and didn't handle potential variations well, which could cause issues when testing across different deployments like Chrome or Google3.

Solution

Refactored the logic into a dedicated helper function _should_use_threaded_ops to improve readability and robustness.

• The feature flag now supports * anywhere in the list to enable threaded operations for all targets in that specific deployment.
• Both the incoming fuzzer name and the configuration list are converted to lowercase, preventing failures due to casing mismatches.
• Flattened the nested conditions in _utask_preprocess by moving the decision logic out.

This prepares the feature for easier rollout and testing across different environments without requiring further code changes.

Note: I also improved a comment as requested in here.

Validation

The wildcard worker in dev:

GCP Link