typo fixes all over the place

found and semi-manually replaced by using:
 codespell -L mut -L crate -i 3 -w

Mostly in comments, but also email notification and two occurrences
of misspelled  'reserved' struct member, which where not used and
cargo build did not complain about the change, soo ...

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

src/backup.rs

@@ -75,7 +75,7 @@
 //!
 //! Since PBS allows multiple potentially interfering operations at the
 //! same time (e.g. garbage collect, prune, multiple backup creations
-//! (only in seperate groups), forget, ...), these need to lock against
+//! (only in separate groups), forget, ...), these need to lock against
 //! each other in certain scenarios. There is no overarching global lock
 //! though, instead always the finest grained lock possible is used,
 //! because running these operations concurrently is treated as a feature