cargo-deny and cargo-machete: four advisories fixed, three unused dependencies gone (#281, #282)

cargo deny check found 10 RustSec advisories in Cargo.lock: ammonia
4.1.4 (three, XSS via SVG animation tags among them), rustls 0.23.44
(five), h2 0.4.15 (one) and ringbuf 0.4.8 (one). cargo update took ammonia
to 4.2.4, rustls to 0.23.46 and h2 to 0.4.20. ringbuf's fix is 0.5, which
librqbit 9.0.1 (the newest) cannot take; its double free needs an element
whose Drop panics and librqbit-utp's buffer holds u8, so deny.toml ignores
it with that reason.

deny.toml allows permissive licences only, crates.io only, and no
wildcard versions; ipx and ipx-directory say publish = false, as feed did.
cargo machete found crates/ipx still listing atom_syndication, quick-xml
and rss, which only crates/feed uses since parsing moved there.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/ipx/CHANGELOG.md

@@ -33,6 +33,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - A 429 from TypeSafe holds every call back as it asks, instead of the pass going on asking (#277).
 - Looking for items to read for Signals read every item on the server on each scan; it now reads only recent ones (#274).
 
+### Security
+
+- ammonia, which cleans publishers' HTML, updated to 4.2.4 for three advisories, among them XSS through SVG animation tags; rustls to 0.23.46 for five and h2 to 0.4.20 for one, in every connection ipx makes (#281).
+
 ## [1.3.0] - 2026-10-16
 
 ### Added