Add Python SWIG bindings (#ifdef SWIGPYTHON)

[lnagel]

Summary

Add Python-specific SWIG typemaps and template instantiations to libcdoc.i, guarded by #ifdef SWIGPYTHON. This follows the same pattern as the existing #ifdef SWIGJAVA block and enables Python bindings (e.g. pycdoc) to consume libcdoc.i directly without patching.

What's included

• %include <exception.i> / %include <stdint.i> — exception.i provides SWIG_exception; stdint.i is required for SWIG to properly resolve uint8_t and size_type inside template instantiations (without it, ByteVector.size() returns an opaque pointer instead of an integer)
• Director typemaps for result_t — enables Python subclasses of DataSource, CryptoBackend, etc. to return result_t values correctly
• Multi-argument typemaps for (const uint8_t *src, size_t size) and (uint8_t *dst, size_t size) — accepts Python bytes/bytearray for writeData/readData calls
• std::vector<uint8_t> typemaps — bidirectional conversion between std::vector<uint8_t> and Python bytes, plus output parameter support (std::vector<uint8_t>& appended as second return value)
• %exception block — translates C++ std::exception to Python RuntimeError
• Template instantiations — ByteVector, ByteVectorVector, StringVector

What's NOT included (already in shared section)

• %include <std_vector.i>, <std_string.i> (lines 39-40)
• %apply for integer types (lines 83-88)
• %feature("director") for all 6 director classes (lines 213-219)
• %template(LockVector) (line 682)

Test plan

• swig -python -c++ -directors -I./cdoc libcdoc.i generates correct Python wrappers
• swig -java -c++ -directors -I./cdoc libcdoc.i produces identical Java output (no regression)
• pycdoc builds and passes 48/48 tests against this branch without any patches

[metsma]

Is there functions where exception is explicitly thrown?
We tried to keep API exception free to simplify binding generation

[lnagel]

I appreciate that the public API is designed to be exception-free using result_t codes — the noexcept try-catch patterns in Io.h and Crypto.cpp confirm that intent.

The %exception block is a defensive safety net rather than a primary error path. Without it, if any C++ exception escapes to Python it would call std::terminate() and abort the entire Python process. With the block, it becomes a catchable RuntimeError instead.

Cases where exceptions could still propagate despite the exception-free API design:

• std::bad_alloc from any std::vector, std::string, or std::make_unique allocation
• Vendored library exceptions — jwt-cpp (ecdsa_exception, rsa_exception, token_verification_exception, etc.), picojson (std::runtime_error, std::bad_cast), and httplib during key server communication
• Base64 decoding in json/base.h throws std::runtime_error on invalid input

It has zero runtime cost in the normal (no-exception) path — just a try/catch frame. Happy to remove it if you prefer to keep the SWIG interface minimal, but it's standard practice for Python bindings as a crash-prevention measure.

[lnagel]

Thanks! This will be promptly released in pycdoc as well (we are currently tracking your master branch)
https://github.com/namespace-ee/pycdoc/releases/tag/v0.1.2