[fix][broker] Fix REST API to produce messages to single-partitioned topics

[Joforde]

Fixes #24442

Motivation

The REST API fails to produce messages to single-partitioned topics (partition count = 1) due to incorrect topic type detection.

Modifications

• Fixed topic type detection condition in TopicsBase to properly handle single-partitioned topics
• Changed from if (!topicName.isPartitioned() && metadata.partitions > 1)
  to if (!topicName.isPartitioned() && metadata.partitions > 0)

Verifying this change

• Make sure that the change passes the CI checks.

This change added tests and can be verified as follows:

• Extended TopicsTest.testProduceToPartitionedTopic test cases with single-partition topic testing.

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

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

Matching PR in forked repository

PR in forked repository: Joforde@408ac9d

[Joforde]

I am doing pulsarbot run-failure-checks

[Joforde]

I am doing pulsarbot run-failure-checks

The tests for BROKER_GROUP_2 were successfully executed using the command:
mvn test -pl pulsar-broker -Dgroups='schema,utils,functions-worker,broker-io,broker-discovery,broker-compaction,broker-naming,broker-replication,websocket,other',
as confirmed by the successful GitHub Actions run:
https://github.com/Joforde/pulsar/actions/runs/15842886147/job/44659112127.