Update rust to 1.68.1 and tarpaulin to 0.25.1

[harrison-tin]

What this PR does / why we need it:

1. Updates rust toolchain to 1.68.1
2. Updates Tarpaulin to 0.25.1

Special notes for your reviewer:

1. New rust version suggests to replace .into_iter().filter().collect() with .retain()
2. Comments cannot have <> or else it fails cargo doc

If applicable:

• this PR has an associated PR with documentation in akri-docs
• this PR contains unit tests
• added code adheres to standard Rust formatting (cargo fmt)
• code builds properly (cargo build)
• code is free of common mistakes (cargo clippy)
• all Akri tests succeed (cargo test)
• inline documentation builds (cargo doc)
• all commits pass the DCO bot check by being signed off -- see the failing DCO check for instructions on how to retroactively sign commits

[kate-goldenring]

Just need to fix the inline docs issue of using <Action> (that is causing the failing Rust Check action) and then LGTM. Also, would be great to follow this up with a PR to akri docs like this one project-akri/akri-docs#41

[harrison-tin]

Just need to fix the inline docs issue of using <Action> (that is causing the failing Rust Check action) and then LGTM. Also, would be great to follow this up with a PR to akri docs like this one project-akri/akri-docs#41

Thanks! Created a PR to update doc project-akri/akri-docs#65