feat(avro-to-json): add wireFormat configuration parameter for deterministic Avro parsing

[katriendg]

Summary

Application: src/500-application/512-avro-to-json
WASM Operator for Azure IoT Operations

Add an optional wireFormat configuration parameter to the avro-to-json operator that lets users declare the wire format of incoming Avro messages. This replaces the current implicit try/fallback approach with deterministic, format-specific parsing when the format is known, while preserving backward-compatible auto-detection as the default.

Motivation

The current parse_with_schema function attempts raw Avro parsing first, and on failure retries after stripping a 5-byte Confluent Schema Registry prefix. This has two problems:

1. Ambiguity — strip_confluent_header triggers on any payload starting with 0x00 longer than 5 bytes. If raw Avro data legitimately starts with 0x00 and fails for an unrelated reason (schema mismatch, truncation), the retry produces a misleading error.
2. Extensibility — other schema registries (Apicurio, Karapace) use different header layouts. Adding more fallback branches creates a fragile chain of guesses.

A wireFormat parameter makes parsing deterministic when the format is known, and keeps the auto fallback for users who prefer zero-config.

Configuration Values

Value	Behavior
auto	Default. Current try-raw-then-strip-and-retry logic (backward-compatible).
confluent	Always strip 5-byte Confluent prefix (0x00 + 4-byte schema ID) before parsing.
raw	Parse directly with no prefix handling. Fail immediately if parsing fails.

Implementation Scope

Rust Code (operators/avro-to-json/src/lib.rs)

• Add WireFormat enum (Auto, Confluent, Raw) and a WIRE_FORMAT OnceLock static
• Parse wireFormat from configuration properties in avro_init
• Refactor parse_with_schema to dispatch on WireFormat instead of implicit try/fallback
• Extract parse_with_schema_inner(data, schema, wire_format) for testability
• Keep strip_confluent_header unchanged
• Add ~7 unit tests covering each variant

Graph YAML

• Add wireFormat parameter to moduleConfigurations in resources/graphs/graph-avro-to-json.yaml

Documentation

• Update configuration table in src/500-application/512-avro-to-json/README.md
• Add "Wire Format" section explaining the three options
• Update Avro Format Detection priority table
• Add troubleshooting entry for Confluent prefix errors
• Update blueprints/full-single-node-cluster/terraform/dataflow-graphs-avro-json.tfvars.example

Files to Modify

File	Change
operators/avro-to-json/src/lib.rs	Add WireFormat enum, static, init parsing, refactor parse_with_schema, add tests
resources/graphs/graph-avro-to-json.yaml	Add wireFormat parameter definition
blueprints/full-single-node-cluster/terraform/dataflow-graphs-avro-json.tfvars.example	Add wireFormat configuration entry
src/500-application/512-avro-to-json/README.md	Config table, Wire Format section, detection table, troubleshooting

Version Impact

Non-breaking, additive change. Default auto behavior matches the current implementation exactly. Existing deployments require no configuration changes. Bump minor version in Cargo.toml.