Rust build caching improvements & fixes

[Porges]

Caches are getting too big and we are exceeding the 10GB limit, leading to cache churning.

1. Try to make the caches smaller by using Swatinem/rust-cache, which is smarter about what gets cached.

   • After doing this it turns out we don't really need sccache any more, it has very little impact upon compile times as the cache hit ratio is low. So remove it, to reduce complexity of build and size of build caches.

2. Also fix artifact caching which had been broken by a version format change (4956cf5).

[codecov-commenter]

Codecov Report

Merging #3197 (ad60413) into main (b1b7cf0) will increase coverage by 3.90%.
The diff coverage is 91.66%.

@@            Coverage Diff             @@
##             main    #3197      +/-   ##
==========================================
+ Coverage   25.63%   29.53%   +3.90%     
==========================================
  Files         152      332     +180     
  Lines       16289    39060   +22771     
==========================================
+ Hits         4175    11535    +7360     
- Misses      12114    27525   +15411     

Impacted Files	Coverage Δ
src/agent/onefuzz/src/libfuzzer.rs	68.26% <91.66%> (ø)

... and 179 files with indirect coverage changes