Enforce lockfile floors for time and bytes

[multiplex55]

Motivation

• Ensure transitive dependencies time and bytes resolve to known-safe minimums to avoid accidental downgrades or incompatibilities.
• Provide an automated, deterministic guard so maintainers can detect lockfile regressions locally and in CI.

Description

• Add explicit dependency floor constraints in Cargo.toml: time = ">=0.3.47, <0.4" and bytes = ">=1.11.1, <2" to express the required minimums.
• Regenerate Cargo.lock so time resolves to 0.3.47 and bytes resolves to 1.11.1 (remove older resolved versions for those crates).
• Add tests/dependency_floor_guard.rs, a deterministic, offline-safe test that parses Cargo.lock, asserts each crate appears exactly once, and verifies time >= 0.3.47 and bytes >= 1.11.1, including a local SemVer helper and unit tests for the helper.
• Update README.md to document the enforcement command for maintainers: cargo test --test dependency_floor_guard.

Testing

• Ran cargo update -p time --precise 0.3.47 && cargo update -p bytes --precise 1.11.1, which succeeded and updated Cargo.lock to the targeted versions.
• Ran a local script to inspect Cargo.lock and confirmed time is 0.3.47 and bytes is 1.11.1.
• Attempted cargo test --test dependency_floor_guard on the environment default toolchain which failed because time 0.3.47 requires rustc 1.88.0.
• Attempted cargo +1.88.0 test --test dependency_floor_guard, which progressed but the build ultimately failed in this Linux environment due to a missing system alsa development library required by a transitive native crate, not due to the guard test logic itself.

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Codex Task