feat: implement Apache Avro decoders

[Copilot]

This PR implements two Apache Avro decoder classes to complement the existing encoder functionality:

AvroDecoder (Lower-level)

A low-level decoder that implements the BinaryJsonDecoder interface and provides methods for decoding specific Avro data types when the schema is known implicitly. Features include:

• Decoding of all Avro primitive types (null, boolean, int, long, float, double, bytes, string)
• Decoding of complex types (arrays, maps, unions, records, enums, fixed-length data)
• Proper variable-length integer decoding with zigzag decoding for signed values
• IEEE 754 float/double decoding with little-endian byte order as required by Avro specification
• Error handling for malformed data and invalid union indices

AvroSchemaDecoder (Higher-level)

A schema-aware decoder that uses AvroDecoder internally and provides validation against Avro schemas. Features include:

• Schema validation during decoding process
• Named schema resolution for records, enums, and fixed types
• Type-safe decoding with schema enforcement
• Helpful error messages for schema mismatches
• Round-trip compatibility with existing AvroSchemaEncoder

Implementation Details

• Follows existing patterns from other codecs in the repository (BencodeDecoder, IonDecoder, etc.)
• Uses the Reader class from @jsonjoy.com/util for binary data reading
• Implements proper Avro binary encoding specification (https://avro.apache.org/docs/1.12.0/specification/)
• Includes comprehensive test coverage with 170+ test cases covering all data types and edge cases
• Maintains backward compatibility and doesn't modify existing code

Usage Example

import {AvroSchemaDecoder, AvroSchemaEncoder} from '@jsonjoy.com/json-pack/lib/avro';
import {Writer} from '@jsonjoy.com/util/lib/buffers/Writer';

const schema = {
  type: 'record',
  name: 'User',
  fields: [
    {name: 'name', type: 'string'},
    {name: 'age', type: 'int'}
  ]
};

const encoder = new AvroSchemaEncoder(new Writer());
const decoder = new AvroSchemaDecoder();

const data = {name: 'Alice', age: 30};
const encoded = encoder.encode(data, schema);
const decoded = decoder.decode(encoded, schema);
// decoded === {name: 'Alice', age: 30}

Fixes #38.

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[streamich]

Do not use beforeEach. To setup a testbed, create a helper function like setup:

  const setup = () => {
    writer = new Writer();
    encoder = new AvroSchemaEncoder(writer);
    decoder = new AvroSchemaDecoder();
    return {writer, encoder, decoder};
  };

Make sure linter and formatter pass.

[streamich]

Do not use beforeEach. To setup a testbed, create a helper function like setup:

Suggested change

	beforeEach(() => {
	writer = new Writer();
	encoder = new AvroSchemaEncoder(writer);
	decoder = new AvroSchemaDecoder();
	});
	const setup = () => {
	writer = new Writer();
	encoder = new AvroSchemaEncoder(writer);
	decoder = new AvroSchemaDecoder();
	return {writer, encoder, decoder};
	};

[Copilot]

Fixed in commit e27ae53. Replaced beforeEach with the suggested setup() helper function pattern. All 28 tests in AvroSchemaDecoder.spec.ts now use const {encoder, decoder} = setup() instead of relying on beforeEach.

[Copilot]

Do not use beforeEach. To setup a testbed, create a helper function like setup:

...

Fixed in commit e27ae53. Replaced beforeEach with setup() helper function in both AvroSchemaDecoder.spec.ts and AvroDecoder.spec.ts files. All tests updated to use the const {encoder, decoder} = setup() pattern. Linter and formatter also pass.

[github-actions]

🎉 This PR is included in version 1.8.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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