Add TypeScript, Python, and PHP code generators

[pcriadoperez]

Summary

Adds SBE code generators for three new target languages: TypeScript, Python, and PHP.

Each generator follows the same architecture as the existing generators (Java, C++, Rust, etc.) and plugs into the standard SBE tool pipeline via TargetCodeGeneratorLoader.

What's included

• TypeScript generator — produces TypeScript interfaces and classes for encoding/decoding SBE messages, with an index file for module exports.
• Python generator — produces Python 3.8+ classes using the struct module for binary serialization, with type hints. Supports a keyword append token (-Dsbe.keyword.append.token=_) for schemas containing Python reserved words.
• PHP generator — produces PHP 8.0+ classes using pack()/unpack() for binary serialization, with union types and typed properties.
• Updated TargetCodeGeneratorLoader to register PYTHON, PHP, and TYPESCRIPT targets.
• Updated README with usage instructions for all three languages.
• Basic encode/decode test scripts for Python and PHP.

Generator files

Each language follows the same structure under sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/{language}/:

• {Language}Generator.java — main code generation logic
• {Language}OutputManager.java — file output management
• {Language}Util.java — language-specific utilities (type mapping, keyword handling, etc.)

How to test

1. Build the SBE tool

./gradlew

2. Generate codecs from a schema

# TypeScript
java -Dsbe.output.dir=output/typescript -Dsbe.target.language=TYPESCRIPT \
  -jar sbe-all/build/libs/sbe-all-*.jar path/to/schema.xml

# Python
java -Dsbe.output.dir=output/python -Dsbe.target.language=PYTHON \
  -jar sbe-all/build/libs/sbe-all-*.jar path/to/schema.xml

# PHP
java -Dsbe.output.dir=output/php -Dsbe.target.language=PHP \
  -jar sbe-all/build/libs/sbe-all-*.jar path/to/schema.xml

3. Run the included test scripts

# Python (requires Python 3.8+)
cd python
python test_order.py

# PHP (requires PHP 8.0+)
cd php
php test_order.php

These scripts encode and decode a simple Order message and verify round-trip correctness.

4. Test with the existing SBE test schemas

You can also generate code against the test schemas bundled in the repo to verify more complex scenarios (groups, vardata, composites, enums):

java -Dsbe.output.dir=output/python -Dsbe.target.language=PYTHON \
  -jar sbe-all/build/libs/sbe-all-*.jar \
  sbe-tool/src/test/resources/code-generation-schema.xml

java -Dsbe.output.dir=output/typescript -Dsbe.target.language=TYPESCRIPT \
  -jar sbe-all/build/libs/sbe-all-*.jar \
  sbe-tool/src/test/resources/code-generation-schema.xml

5. Verify existing tests still pass

./gradlew test