c27c125e

By: Ben Ruijl <ben@ruijl.ch>

fix spynso pyodide compilation

Separate portable and native features through the Python adapter and HEP
library, gate native evaluator exports and stubs, and add a WASM build check.

Original user request:

Fix the Python WASM compilation for spynso, so that it works with pyodide.

```
# One-time setup
python3.14 -m venv .venv-wasm
source .venv-wasm/bin/activate
pip install pyodide-build==0.39.0 maturin==1.15.0

export PYODIDE_XBUILDENV_PATH="$HOME/.cache/symbolica-pyodide"
pyodide xbuildenv install 314.0.7
export RUSTUP_TOOLCHAIN="$(pyodide config get rust_toolchain)"
rustup toolchain install "$RUSTUP_TOOLCHAIN" \
  --profile minimal --target wasm32-unknown-emscripten
```

```
pyodide build . --outdir dist --no-isolation \
  -C maturin.build-args="--locked --profile release-small \
  --no-default-features --features wasm \
  -- -C link-arg=-sEXPORTED_FUNCTIONS=_PyInit_core"
```

pyodide build . --outdir dist --no-isolation \
  -C maturin.build-args="--locked --profile release-small \
  --no-default-features --features wasm \
  -- -C link-arg=-sEXPORTED_FUNCTIONS=_PyInit_core"

Follow-up request:

Create the PR