[FLINK-36298][table] Fix NullPointerException in metadata query supplier on fresh threads

[Au-Miner]

What is the purpose of the change

Fix a flaky NullPointerException raised from Calcite's RelMetadataQueryBase.getMetadataHandlerProvider during Volcano-based query optimization, surfaced as a PyFlink test failure when planning runs on a thread that has never initialized THREAD_PROVIDERS.

Brief change log

• Update the metadata query supplier in FlinkRelOptClusterFactory.create to set RelMetadataQueryBase.THREAD_PROVIDERS before constructing FlinkRelMetadataQuery, so the parent RelMetadataQuery constructor sees a non-null JaninoRelMetadataProvider regardless of which thread invokes the supplier.
• Cache the JaninoRelMetadataProvider instance at object init to avoid re-wrapping FlinkDefaultRelMetadataProvider on every supplier call.

Verifying this change

Added FlinkRelOptClusterFactoryTest#testMetadataQuerySupplierUsableOnFreshThread, which spawns a fresh thread, clears THREAD_PROVIDERS, invokes the cluster's supplier, and asserts that the produced RelMetadataQuery has a non-null metadataHandlerProvider — the precondition that prevents the NPE in subsequent metadata calls.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API, i.e., is any changed class annotated with @Public(Evolving): no
• The serializers: no
• The runtime per-record code paths (performance sensitive): no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: no
• The S3 file system connector: no

Documentation

• Does this pull request introduce a new feature? no
• If yes, how is the feature documented? not applicable

[flinkbot]

CI report:

• f9ff781 Azure: SUCCESS

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