[FLINK-40972][table] Do not generate cast classes in case of Identity casts

[snuyanzin]

What is the purpose of the change

The idea is to stop generation of dummy CastExecutor classes in case of identity casts
for instance in case of TPCDS query8 it generates 400 classes like that

Brief change log

CastRuleProvider

Verifying this change

test added

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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[flinkbot]

CI report:

• d58d642 Azure: SUCCESS

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[fhueske]

Thanks for the improvement @snuyanzin!

+1 to merge once CI passes.

Cheers, Fabian