[fix][broker] Use compatible Avro name validator to allow '$' in schema record names

[mattisonchao]

Motivation

After #24617 upgraded Avro to a newer version, the default Schema.Parser()
uses UTF_VALIDATOR which rejects the $ character in record names. This
breaks Protobuf schemas whose Avro representation contains $ in generated
nested type names (e.g. inner classes).

Modifications

• Introduce a CompatibleNameValidator that allows $ in addition to letters,
  digits, and underscores, matching the previous Avro behavior.
• Apply the custom validator to all broker-side Schema.Parser() instances
  that handle Protobuf schemas:
  • StructSchemaDataValidator
  • SchemaRegistryServiceImpl
  • AvroSchemaBasedCompatibilityCheck
• Add DataRecord.proto for test reproduction.
• Add unit tests for the CompatibleNameValidator and Protobuf schema
  compatibility.

Note: The client-side SchemaUtil already uses NameValidator.NO_VALIDATION.
A shared solution across broker and client (e.g. factory in pulsar-common)
can be addressed in a follow-up.

Verifying this change

• Unit tests added for CompatibleNameValidator (valid names, invalid names,
  edge cases, error messages).
• Integration test with ProtobufSchema<DataRecord> to reproduce the original issue.
• CI checks pass.

Documentation

• doc-not-needed

[Copilot]

Pull request overview

This PR addresses a regression introduced by the Avro upgrade (1.12.0) where Protobuf-derived Avro schemas can fail parsing due to $ appearing in generated record names, by introducing a more permissive Avro NameValidator and adding tests to cover the scenario.

Changes:

• Add a custom Avro NameValidator (CompatibleNameValidator) to allow $ in Avro record/field names during schema validation.
• Add unit tests for the validator’s behavior and a reproduction test using a generated Protobuf schema.
• Introduce a new Protobuf message (DataRecord.proto) used by the tests.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
pulsar-broker/src/main/java/org/apache/pulsar/broker/service/schema/validator/StructSchemaDataValidator.java	Uses a custom Avro NameValidator to accept $ during schema parsing/validation.
pulsar-broker/src/test/java/org/apache/pulsar/broker/service/schema/validator/SchemaDataValidatorTest.java	Adds tests for the new validator and a Protobuf-based reproduction.
pulsar-broker/src/main/proto/DataRecord.proto	Adds a Protobuf schema used to generate Avro with nested-type $ names for testing.

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[lhotari]

is this file for tests? I think it should be in pulsar-broker/src/test/proto directory in that case.