[FLINK-40492][table] Support casting from VARIANT to TIME and nanosecond timestamps - #29080

What is the purpose of the change

Extends VARIANT-to-scalar casting to the temporal types added in FLINK-40491: TIME and nanosecond-precision TIMESTAMP / TIMESTAMP_LTZ.
A VARIANT holding such a value can now be cast to TIME(3), TIMESTAMP(9), TIMESTAMP_LTZ(9) and to a string, with CAST failing / TRY_CAST returning NULL on a kind mismatch.

Brief change log

• Enable CAST / TRY_CAST from VARIANT to TIME
• Accept the TIMESTAMP_NS / TIMESTAMP_LTZ_NS storage kinds when casting to TIMESTAMP(p) / TIMESTAMP_LTZ(p)
• Render TIME / TIMESTAMP_NS / TIMESTAMP_LTZ_NS when casting VARIANT to a string
• Update the cast-support matrix in the docs

Verifying this change

This change added tests in CastRulesTest (VARIANT → TIME/TIMESTAMP(9)/TIMESTAMP_LTZ(9), both storage kinds, plus string rendering), LogicalTypeCastsTest and CastRuleProviderTest.

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? yes (new castable type pairs for VARIANT)
• If yes, how is the feature documented? docs (cast-support matrix)

Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)

Generated-by: Claude Code (Claude Opus 4.8)