[FLINK-39384][python] Fix Java errors when trying to load or compile a CompiledPlan

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What is the purpose of the change

When trying to load or compile a CompiledPlan in the Python Table API, an error occurs because the underlying CompiledPlan's self reference is erroneously set to the underlying java object, rather than the python one.

Brief change log

• Fixed incorrect object reference when loading/compiling a CompiledPlan in the Python Table API.

Verifying this change

This change added tests and can be verified as follows:

• Added tests to explicitly test loading and compiling a CompiledPlan.

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)

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CI report:

• d09507c Azure: SUCCESS

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