v0.15.2: pin setuptools<81 so the chatterbox watermarker loads

chatterbox-turbo died with "TypeError: 'NoneType' object is not callable" at
model load. resemble-perth 1.0.1 needs pkg_resources, which setuptools dropped
in 81; the CUDA lock had resolved setuptools transitively to 82.0.1. Upstream
swallows the ImportError and leaves PerthImplicitWatermarker as None, so the
failure surfaced only on the first synthesis request.

scripts/heavy-deps-cuda.in now constrains setuptools<81 (lock resolves 80.10.2,
no other package moved), and Dockerfile.cuda asserts the watermarker is
constructible at build time so this fails the build rather than a request.

See CHANGELOG.md for the full entry.