Pulsar: built-in Avro schema support (typed ISchema<T>) (#3213)

[jeremydmiller]

Closes #3213. Follow-up to the JSON schema work (#3210), completing the Pulsar schema story from #3183.

JSON used a pass-through schema where Wolverine owns the body bytes. Avro can't work that way — DotPulsar's Schema.AvroISpecificRecord<T>() owns the encode/decode, so the body must be genuine Avro on the wire. This adds a small codec seam that keeps the existing byte-oriented sender/listener (and all the ack/retry/DLQ logic) fully intact.

opts.PublishMessage<OrderPlaced>().ToPulsarTopic(topic).UseAvroSchema<OrderPlaced>();
opts.ListenToPulsarTopic(topic).UseAvroSchema<OrderPlaced>();

How it works

• IPulsarMessageCodec / PulsarAvroCodec<T> wraps DotPulsar's built-in Schema.AvroISpecificRecord<T>(). T must be an Apache.Avro ISpecificRecord at runtime — there is no compile-time Avro dependency in the transport (DotPulsar resolves the schema reflectively from the type's static _SCHEMA).
• UseAvroSchema<T>() sets endpoint.MessageCodec and a pass-through PulsarSchema carrying the Avro SchemaInfo, so the broker registers the Avro schema for the topic.
• PulsarSender encodes envelope.Message through the codec (falling back to Wolverine's serialized body for non-codec messages such as a ping); PulsarListener decodes to the message object and sets envelope.Message directly — the pipeline then skips its own body deserialization (HandlerPipeline.TryDeserializeEnvelope returns early when Message is already set).

This reuses the UsePulsarSchema(...) seam direction noted in #3210; Protobuf/other schema types can plug in the same way via a custom codec.

Acceptance criteria (from #3183 / #3213)

• ✅ Avro path demonstrated: end-to-end publish/consume under an Avro schema with broker-side AVRO schema registration, verified via the Pulsar admin REST endpoint returning type: AVRO.
• ✅ JSON schema path unchanged — no regression (re-verified green).

Tests / build

• pulsar_avro_schema: codec round-trip (unit) + end-to-end broker round-trip with AVRO registration — green against a Testcontainers broker. Apache.Avro added to the test project only.
• Full wolverine.slnx builds clean in Release.

🤖 Generated with Claude Code

[jeremydmiller]

Superseded by the rebased branch (resolves conflicts with the merged dedup PR #3212). See the replacement PR.