error[E0554]: `#![feature]` may not be used on the stable release channel
 --> generic-rt/src/lib.rs:3:1
  |
3 | #![feature(core_intrinsics)]
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

I'm trying to package a python package using maturin in nixpkgs.
I use

  cargoDeps = rustPlatform.fetchCargoVendor {
    inherit
      pname
      version
      src
      sourceRoot
      cargoRoot
      ;
    hash = "sha256-m3SNWjHsQcrH6v8Z6CnURhuXNQRgvtGreM0g91rOv6Q=";
  };

But it fails with

Executing maturinBuildHook
maturinBuildHook flags: --jobs=64 --offline --target x86_64-unknown-linux-gnu --manylinux off --strip --release --out /build/source/obstore/dist --interpreter python3.13
error: failed to load source for dependency `object_store`

Caused by:
  Unable to update https://github.com/apache/arrow-rs-object-store?rev=f422dce1528ee2a089d8061af639c3f2a9cd43af#f422dce1

Caused by:
  can't checkout from 'https://github.com/apache/arrow-rs-object-store': you are in the offline mode (--offline)
💥 maturin failed

The Cargo.lock has this at the end:

[[patch.unused]]
name = "object_store"
version = "0.12.2"
source = "git+https://github.com/apache/arrow-rs-object-store?rev=f422dce1528ee2a089d8061af639c3f2a9cd43af#f422dce1528ee2a089d8061af639c3f2a9cd43af";

Am I supposed to do something extra to fetch this dep?