[worker:deadcode:rust] remove unused chrono dependency - #594

Resolves the agent:deadcode:rust finding in #593 by removing the unused chrono dependency from crates/minimald/Cargo.toml.

What changed

• Dropped chrono.workspace = true from crates/minimald [dependencies]. A grep across the entire minimald crate for every chrono usage pattern (chrono::, Utc, DateTime, NaiveDate, Datelike, Timelike, ...) found no references — only the substring inside "synchronously"/"asynchronous" comments. The machete HIGH-confidence finding is accurate.
• Regenerated Cargo.lock; chrono stays as a transitive dependency of other crates, so only minimald's direct edge is removed.

Candidates intentionally NOT changed

The issue also lists prost, prost-types, tonic, and tonic-prost (remote-proto) as HIGH machete dep candidates, with a triage note suggesting they move to [build-dependencies]. These are machete false positives: crates/remote-proto/src/lib.rs pulls the generated protobuf/gRPC code in via include!(concat!(env!("OUT_DIR"), ...)), and that generated code references ::prost::, ::tonic::, and the tonic-prost codec at runtime. machete cannot see those references because they live in OUT_DIR, not in the scanned .rs sources. Moving the four crates to [build-dependencies] (or removing them) would break compilation of remote-proto, so they are left for human review. prost-build/tonic-prost-build are already correctly in [build-dependencies] (the issue notes no action needed).

Verification

• cargo build -p minimald --all-targets (from ./target) passed (exit 0): minimald and every crate it depends on compile cleanly without chrono. Because chrono was a private dependency of minimald, removing it cannot affect any other crate, so this targeted build fully covers the change.
• Note: an initial cargo build --workspace --all-targets aborted with No space left on device (os error 28) while linking unrelated test targets — a runner disk-exhaustion limitation, not a compile error from this change. After reclaiming the incremental-compile cache, the targeted build completed successfully.
• No .rs files were modified, so cargo fmt is a no-op for this change.
• The host backstop re-runs the full gate (cargo fmt --all --check, cargo build --workspace --all-targets --locked, cargo clippy --workspace --all-targets --locked -- -D warnings, cargo test --workspace --all-targets --locked) before this PR opens.

Closes #593

Generated by Chore-issue worker agent (side-repo-ops operator) · ◷

Summary by CodeRabbit

• Chores
  • Removed an unused dependency declaration from the build configuration.
  • No visible product behavior changed.