Increase recommended Rust toolchain to 1.78.0

[mulkieran]

• [x] Fix any newly introduced compiler or clippy errors (CLIPPY_FIX=1 make clippy and refine procedure for automatically applying clippy changes):

  • [x] devicemapper-rs
  • [x] libblkid-rs
  • [x] libcryptsetup-rs
  • [x] loopdev-3
  • [x] stratisd: https://github.com/stratis-storage/stratisd/pull/3605

• [x] Give karma for f39 and f40 Rust release:

  • [x] f39: https://bodhi.fedoraproject.org/updates/FEDORA-2024-ac4cfc5ad3
  • [x] f40: https://bodhi.fedoraproject.org/updates/FEDORA-2024-7194268cb4

• [x] Bump current development toolchain in GitHub workflows

  • [x] devicemapper-rs
  • [x] libblkid-rs
  • [x] libcryptsetup-rs
  • [x] loopdev-3
  • [x] stratisd
  • [x] stratis-cli