[FLINK-39789] AvroSchemaConverter updates for local-timestamp-* and timestamp-nanos logical types

[Shekharrajak]

Fix FLINK-39789.

What is the purpose of the change

AvroSchemaConverter.convertToDataType(String) and convertToTypeInfo(String) — the only public Avro→Flink type-mapping entry points — silently dropped the logical type for local-timestamp-millis and local-timestamp-micros and returned BIGINT / Long, producing a Flink RowType that is incompatible with TimestampData at runtime.

The internal two-arg overloads contained branches for local-timestamp-*, but only on the legacyTimestampMapping=false arm. The single-arg public APIs hard-code legacyTimestampMapping=true, so those branches were unreachable from any public API.

Brief change log

Verifying this change

• AvroSchemaConverter.convertToDataType(Schema, boolean) — hoist localTimestampMillis / localTimestampMicros checks above the legacyMapping switch so they are honoured in both modes.
• AvroSchemaConverter.convertToTypeInfo(Schema, boolean) — identical hoist, mapping to Types.LOCAL_DATE_TIME.
• Add AvroSchemaConverterLocalTimestampBehaviorTest — 13 tests covering the single-arg public API, the two-arg overloads in both modes, the convertToTypeInfo mirror, the JIRA's exact runtime ClassCastException reproducer, and a round-trip sanity check.
• Update AvroSchemaConverterTest.validateLegacyTimestampsSchema(...) helpers — they previously hard-coded Types.LONG / BIGINT for local_timestamp_* (asserting the bug); now assert the spec-correct Types.LOCAL_DATE_TIME / TIMESTAMP(p).

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

• Dependencies (does it add or upgrade a dependency): (yes / no) no
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)no
• The serializers: (yes / no / don't know)no
• The runtime per-record code paths (performance sensitive): (yes / no / don't know)no
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (yes / no / don't know)no
• The S3 file system connector: (yes / no / don't know)no

Documentation

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

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CI report:

• dc5e6de Azure: FAILURE

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[Shekharrajak]

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