Update Rust edition to 2021 across all crates

[Porges]

Changes mostly done by cargo fix --edition.

[codecov-commenter]

Codecov Report

Merging #3392 (8c4ef33) into main (d53646e) will decrease coverage by 0.02%.
The diff coverage is 21.42%.

@@            Coverage Diff             @@
##             main    #3392      +/-   ##
==========================================
- Coverage   34.70%   34.68%   -0.02%     
==========================================
  Files         302      302              
  Lines       36917    36920       +3     
==========================================
- Hits        12811    12805       -6     
- Misses      24106    24115       +9     

Files Changed	Coverage Δ
src/agent/onefuzz-agent/src/heartbeat.rs	0.00% <ø> (ø)
src/agent/onefuzz-agent/src/main.rs	0.00% <ø> (ø)
src/agent/onefuzz-agent/src/panic.rs	0.00% <0.00%> (ø)
src/agent/onefuzz-agent/src/scheduler.rs	53.97% <0.00%> (ø)
src/agent/onefuzz-telemetry/src/lib.rs	2.14% <0.00%> (ø)
src/agent/onefuzz/src/auth.rs	31.95% <0.00%> (ø)
src/agent/onefuzz/src/az_copy.rs	0.00% <0.00%> (ø)
src/agent/onefuzz/src/triage.rs	0.00% <ø> (ø)
src/agent/onefuzz/src/blob/url.rs	72.29% <33.33%> (ø)
src/agent/onefuzz/src/expand.rs	81.40% <100.00%> (ø)

... and 2 files with indirect coverage changes