chore: upgrade rust-toolchain to nightly-2025-11-20 (#1214)

## Summary

We want to upgrade the current toolchain to a new one (e.g.
`nightly-2025-11-20`).

However, the recent nightly toolchains already include this
[PR](rust-lang/rust#144443) to introduce a
breaking change s.t. the `target-pointer-width` in
`ceno_rt/riscv32im-ceno-zkvm-elf.json` is integer rather than string.

### Additional changes 
With `nightly-2025-11-20`, the feature `panic_immediate_abort` is now a
real panic strategy. Therefore we have to make changes in the script for
cross building `rv32im` ELF.

Author: kunxian-xia

.github/workflows/lints.yml

@@ -25,7 +25,7 @@ jobs:
           components: rustfmt, clippy
           targets: riscv32im-unknown-none-elf
           # TODO: figure out way to keep this in sync with rust-toolchain.toml automatically
-          toolchain: nightly-2025-08-18
+          toolchain: nightly-2025-11-20
       - name: Cargo cache
         uses: actions/cache@v4
         with:

.github/workflows/tests.yml

@@ -24,7 +24,7 @@ jobs:
         with:
           targets: riscv32im-unknown-none-elf
           # TODO: figure out way to keep this in sync with rust-toolchain.toml automatically
-          toolchain: nightly-2025-08-18
+          toolchain: nightly-2025-11-20
       - name: Cargo cache
         uses: actions/cache@v4
         with:

Cargo.lock

@@ -46,7 +46,7 @@ gkr_iop = { path = "../gkr_iop" }
 mpcs.workspace = true
 
 [build-dependencies]
-vergen-git2 = { version = "1", features = ["build", "cargo", "rustc", "emit_and_set"] }
+vergen-git2 = { version = "9.1.0", features = ["build", "cargo", "rustc", "emit_and_set"] }
 
 [features]
 gpu = ["gkr_iop/gpu", "ceno_zkvm/gpu", "ceno_recursion/gpu", "dep:openvm-cuda-backend", "openvm-native-circuit/cuda"]

ceno_cli/Cargo.toml

@@ -78,12 +78,13 @@ pub fn search_workspace_root<P: AsRef<Path>>(path: P) -> anyhow::Result<PathBuf>
 pub fn get_rust_flags() -> String {
     const BASE_RUST_FLAGS: &[&str] = &[
         "-C",
-        "panic=abort",
+        "panic=immediate-abort",
         "-C",
         "link-arg=-Tmemory.x",
         "-C",
         "link-arg=-Tceno_link.x",
         "-Zlocation-detail=none",
+        "-Zunstable-options",
         "-C",
         "passes=lower-atomic",
         "--cfg",
@@ -104,7 +105,7 @@ pub fn apply_cargo_build_std_args(command: &mut Command) {
         "-Z",
         "build-std=alloc,core,compiler_builtins,std,panic_abort,proc_macro",
         "-Z",
-        "build-std-features=compiler-builtins-mem,panic_immediate_abort,default",
+        "build-std-features=compiler-builtins-mem,default",
     ];
     command.args(BASE_CARGO_ARGS);
 }

ceno_cli/src/utils.rs

@@ -28,5 +28,5 @@
   "singlethread": true,
   "target-c-int-width": 32,
   "target-endian": "little",
-  "target-pointer-width": "32"
+  "target-pointer-width": 32
 }

ceno_rt/riscv32im-ceno-zkvm-elf.json

@@ -1,5 +1,5 @@
 use ceno_zkvm::precompiles::{run_bitwise_keccakf, setup_bitwise_keccak_gkr_circuit};
-use clap::{Parser, command};
+use clap::Parser;
 use ff_ext::GoldilocksExt2;
 use itertools::Itertools;
 use mpcs::BasefoldDefault;

ceno_zkvm/src/bin/bitwise_keccak.rs

@@ -1,5 +1,5 @@
 use ceno_zkvm::precompiles::{run_lookup_keccakf, setup_lookup_keccak_gkr_circuit};
-use clap::{Parser, command};
+use clap::Parser;
 use ff_ext::GoldilocksExt2;
 use itertools::Itertools;
 use mpcs::BasefoldDefault;

ceno_zkvm/src/bin/lookup_keccak.rs

@@ -389,6 +389,7 @@ impl<E: ExtensionField> ProtocolBuilder<E> for KeccakLayout<E> {
         // iterator over split witnesses
         let mut rotation_witness = rotation_witness.iter();
 
+        #[allow(clippy::needless_range_loop)]
         for i in 0..5 {
             #[allow(clippy::needless_range_loop)]
             for j in 0..5 {