bump rust toolchain

Dependencies

• [2] 6YZAVBWU Initial commit
• [3] KLR5FRIB add fs state read/write of repos
• [4] KQABQCCZ update rust to 1.88
• [5] WXQBBQ2A update nightly
• [6] Y6LXBCJB update toolchain and rust edition

Change contents

• replacement in rust-toolchain.toml at line 2
  [3.2173]→[4.2:21](∅→∅)
  − channel = "1.88.0"
  [3.2173]
  + channel = "1.91.1"
• replacement in justfile at line 11
  [2.181]→[5.19:51](∅→∅)
  − nightly := "nightly-2025-07-15"
  [2.181]

  [2.181]
  + nightly := "nightly-2025-11-17"