ZSTD_NO_FORWARD_PROGRESS_MAX is a compile-time override that was returned
directly by the C adapter. Keep the active build value in C, where
configuration belongs, but pass it through an ABI-checked scalar projection to
Rust. Rust now owns the policy boundary and preserves the exact configured
threshold, while the existing stalled-stream comparison, error mapping, and
private DCtx layout remain unchanged.
Test Plan:
- `git diff --cached --check` -- passed
- Cargo, make, builds, native tests, and heavy verification were not run per
request.
ddidderr
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