chore: bump rustfmt toolchain to nightly-2025-12-06

Bumping the toolchain version as part of a git subtree push.

current toolchain (nightly-2025-04-02):

- 1.88.0-nightly (e2014e876 2025-04-01)

latest toolchain (nightly-2025-12-06):

- 1.94.0-nightly (ba86c0460 2025-12-06)

Author: jieyouxu

rust-toolchain

@@ -1,3 +1,3 @@
 [toolchain]
-channel = "nightly-2025-04-02"
+channel = "nightly-2025-12-06"
 components = ["llvm-tools", "rustc-dev"]