Automatic toolchain upgrade to nightly-2025-10-19 (#4420)

Update Rust toolchain from nightly-2025-10-18 to nightly-2025-10-19
without any other source changes.

---------

Co-authored-by: tautschnig <1144736+tautschnig@users.noreply.github.com>
Co-authored-by: Michael Tautschnig <tautschn@amazon.com>

Author: github-actions[bot]

kani-compiler/src/codegen_aeneas_llbc/mir_to_ullbc/mod.rs

@@ -1014,7 +1014,6 @@ impl<'a, 'tcx> Context<'a, 'tcx> {
             let traitref = self
                 .tcx
                 .impl_trait_ref(impl_defid_internal)
-                .unwrap()
                 .skip_binder()
                 .args
                 .first()

rust-toolchain.toml

@@ -2,5 +2,5 @@
 # SPDX-License-Identifier: Apache-2.0 OR MIT
 
 [toolchain]
-channel = "nightly-2025-10-18"
+channel = "nightly-2025-10-19"
 components = ["llvm-tools", "rustc-dev", "rust-src", "rustfmt"]