Add shleder/vetto to Security tools

[shleder]

Project Addition: shleder/vetto

• Entry: * [shleder/vetto](https://github.com/shleder/vetto) [[vetto](https://crates.io/crates/vetto)] - Daemon-less, sub-4ms cold start kernel sandbox for AI coding agents (Landlock, seccomp, namespaces) [![CI](https://github.com/shleder/vetto/actions/workflows/ci.yml/badge.svg?branch=main)](https://github.com/shleder/vetto/actions/workflows/ci.yml)
• Category: ### Security tools (alphabetical order after timescale/rsigma)

Popularity Metrics & CONTRIBUTING.md Compliance

Per CONTRIBUTING.md ("at least 50 stars on GitHub, 2000 downloads on crates.io, or an equivalent level of other popularity metrics"):

1. 8,370+ monthly downloads on npm: @shledery/vetto (distributes pre-compiled platform binaries).
2. 645 downloads on crates.io: vetto.
3. 44 stars on GitHub: shleder/vetto.

Total downloads exceed the 2,000 threshold under the alternative popularity metrics clause. Entry adheres strictly to template and alphabetical sorting rules.

[palfrey]

Total downloads exceed the 2,000 threshold under the alternative popularity metrics clause.

Please add an entry to POPULARITY_OVERRIDES with a comment about where to check the downloads at https://github.com/rust-unofficial/awesome-rust/blob/main/src/main.rs#L107 to enable this.

[shleder]

Added entry to POPULARITY_OVERRIDES in src/main.rs referencing the npm download metrics.