Release echidna 0.11.0 + echidna-optim 0.13.1 (coordinated)

[gvonness-apolitical]

Summary

• Bumps echidna 0.10.0 → 0.11.0 — minor per SemVer: the release adds new public API (the simba trait impls for DualVec<F, N> from Implementation of simba traits for DualVec #38, letting DualVec be used as a scalar inside nalgebra matrices).
• Bumps echidna-optim 0.13.0 → 0.13.1 — coordinated release; its echidna dependency follows to 0.11.0.
• Moves the [Unreleased] CHANGELOG entry into [0.11.0]; updates the SECURITY.md supported-versions table and the README.md install snippets.

No source code changes — version metadata and release notes only.

Test plan

• cargo fmt --check and cargo clippy --all-targets -- -D warnings — clean
• cargo build + full cargo test for both crates (CI feature set) — all green
• cargo doc with RUSTDOCFLAGS=-D warnings — clean
• After merge: tag v0.11.0 → publish.yml validates the tag against echidna's version, publishes both crates to crates.io, and creates the GitHub Release from the [0.11.0] CHANGELOG section