Enable `rkyv`'s strict feature

[nagisa]

Upgrading the toolchain today may change the encoding of the near-vm executables due to rkyv's strict feature not being enabled. This means that any time users build and run neard with a version of rustc toolchain other than what's specified in the rust-toolchain file, they are exposing themselves to invalid execution and, likely, crashes.

Upstream has expressed an intent to make this feature the default, but before that happens we can make an effort to remove this class of footguns ourselves by enabling the strict feature now. This disables rkyv encoding for Rust tuples, though, which we use across near-vm, so those would need additional code changes to adapt.

(There are also other complications with wasmer2, which must not unify this feature due to its own use of tuples…)

[jakmeier]

As a hacky solution addressing the same problem, could we also include the rust compiler version in the vm hash? Not sure if we would want to tolerate the implied inefficiency of forcing a recompilation on each release, though. I'm just trying to list our options.