chore: bump rustfmt toolchain to nightly-2025-04-01

Bumping the toolchain version as part of a git subtree push

current toolchain (nightly-2025-01-02):
  - 1.85.0-nightly (45d11e51b 2025-01-01)

latest toolchain (nightly-2025-04-01):
  - 1.88.0-nightly (0b45675cf 2025-03-31)

Author: rustfmt bot

rust-toolchain

@@ -1,3 +1,3 @@
 [toolchain]
-channel = "nightly-2025-01-02"
+channel = "nightly-2025-04-01"
 components = ["llvm-tools", "rustc-dev"]