Implement Pickler for serialization

[aaa4xu]

Hi there!

This pull request introduces new feature to the library: a Pickler class that enables the serialization of JavaScript objects into the Python pickle format. This complements the existing Parser and makes the library a complete, two-way solution for handling pickle data in a JS/TS environment.

Summary of Changes

Refactored BufferReader to use a shared Sizes enum.

• Replaced magic numbers for data type sizes with a Sizes enum. This enum is now shared between the reader and writer.

BufferWriter class and IWriter interface (src/writer.ts)

• A helper class for writing binary data to a dynamically growing buffer, serving as the counterpart to BufferReader.

Pickler class (src/pickler.ts)

• The core serialization logic resides here
• Handles JavaScript primitives (null, boolean, number, string, bigint)
• Supports container types (Array, Object, Map) and correctly serializes them as Python list and dict.
• Includes memoization to correctly handle shared object references and cyclical data structures (for protocols 1+).

Added tests for the Pickler

• Unit Tests: Verifies the "round-trip" consistency (pickler.dump() -> parser.parse()) for supported data types and protocols.
• Integration Tests: A new suite of tests that serialize data with Pickler and then successfully deserialize it using a standard Python pickle.loads.

I'm excited about this contribution and believe it will be a valuable addition to the project. I'm happy to discuss any part of the implementation or make any necessary changes.

Thanks for your time and consideration.