feat: implement Apache Avro encoder with schema validation

[Copilot]

This PR implements a complete Apache Avro binary encoder for the json-pack library, following the Apache Avro 1.12.0 specification.

Implementation

The implementation includes three main components:

1. AvroSchemaValidator

A comprehensive schema validator that validates Avro schemas and ensures values conform to their schemas:

const validator = new AvroSchemaValidator();
const schema = {
  type: 'record',
  name: 'User',
  fields: [
    {name: 'id', type: 'int'},
    {name: 'name', type: 'string'}
  ]
};

validator.validateSchema(schema); // true
validator.validateValue({id: 123, name: 'John'}, schema); // true

2. AvroEncoder

A basic Avro binary encoder implementing the BinaryJsonEncoder interface for encoding values without schema validation:

const writer = new Writer();
const encoder = new AvroEncoder(writer);
const encoded = encoder.encode({name: 'test', value: 42});

3. AvroSchemaEncoder

A schema-aware encoder that validates values against schemas before encoding:

const schemaEncoder = new AvroSchemaEncoder(writer);
const encoded = schemaEncoder.encode(userData, userSchema);

Key Features

• Complete Avro binary encoding: Supports all Avro types including primitives, records, enums, arrays, maps, unions, and fixed-length data
• Proper encoding semantics: Uses zigzag encoding for signed integers, IEEE 754 for floats, variable-length encoding for lengths, and UTF-8 for strings
• Schema validation: Comprehensive validation of both schemas and values against schemas
• Type safety: Full TypeScript support with detailed type definitions for all Avro schema types
• Error handling: Clear error messages for invalid schemas and non-conforming values
• Union type support: Automatic type detection or explicit index selection for union types

Testing

Added 112 comprehensive test cases covering:

• All primitive and complex Avro types
• Schema validation edge cases
• Value validation against schemas
• Binary encoding correctness
• Error conditions and edge cases

All existing tests continue to pass, ensuring no regressions.

Fixes #41.

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[streamich]

De-reference this.writer only once:

const writer = this.writer;

[streamich]

Do it everywhere in the code: de-reference pointers only once, where possible. Performance is the number one feature of this library.

[Copilot]

Done. Optimized all performance-critical methods to cache this.writer to local variables to reduce property access overhead. Commit d6842c4

[Copilot]

Implemented throughout the codebase. All writer access patterns in hot paths now use local variable caching for better performance. Commit d6842c4

[streamich]

DO NOT use TextEncoder it is very slow. The Writer has fast string encoding methods. Or see other codec implementations.

[Copilot]

Replaced TextEncoder with Writer's native utf8() method for much faster string encoding. The implementation now reserves space for the length prefix, writes the string, then fills in the actual byte count. Commit d6842c4

[streamich]

Do not use ForOfLoop use plain ForLoop, it is faster.

[Copilot]

Converted all for-of loops to plain for loops throughout both AvroEncoder and AvroSchemaEncoder for better performance. Commit d6842c4

[streamich]

The Writer instance should have a way to write .ascii() strings, see other code for reference.

[Copilot]

Updated writeAsciiStr to use Writer's ascii() method for faster ASCII string encoding instead of the generic UTF-8 path. Commit d6842c4

[streamich]

In these primitive encoding methods, we should specify the specific schema type, no? In this case AvroNullSchema.

[Copilot]

Added specific AvroNullSchema type to the writeNull method signature and imported the type for better type safety. Commit d6842c4

[streamich]

When done, make sure tests pass, linter and formatter pass.

[Copilot]

When done, make sure tests pass, linter and formatter pass.

All checks now pass:
✅ Tests: 2833 tests passing
✅ Linter: TSLint clean
✅ Formatter: Prettier clean

Fixed formatting issues in the Avro implementation files. Commit 6b9bd54

[github-actions]

🎉 This PR is included in version 1.6.0 🎉

The release is available on:

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

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