README getting-started GF(2) example crashes because rho0w is not scalar-safe

[terasakisatoshi]

Summary

The README's main getting-started example crashes as written.

At README.rst:78-79, the example defines:

def rho0w(w):
    return np.sqrt(1-w.clip(-1,1)**2) * 2/np.pi

During the documented flow, basis.v.overlap(rho0w) calls rho0w with a scalar float, so w.clip(...) raises an exception before the solver loop starts.

Reproduction

On commit 75b9f8fbb7991f09867e64d19424868a1c598f63:

uv sync
uv run python - <<'PY'
import sparse_ir, numpy as np
basis = sparse_ir.FiniteTempBasis('F', beta=10, wmax=8, eps=1e-6)
def rho0w(w):
    return np.sqrt(1-w.clip(-1,1)**2) * 2/np.pi
basis.v.overlap(rho0w)
PY

Actual

AttributeError: 'float' object has no attribute 'clip'

Expected

The README example should run verbatim.

Notes

Using np.clip(w, -1, 1) instead of w.clip(-1, 1) makes the full README GF(2) path run successfully in my test run.