Add support for uint16x4x4_t AArch64 SIMD type family

[google-labs-jules]

Added uint16x4x2_t, uint16x4x3_t, and uint16x4x4_t to src/impls.rs.
Verified changes using ./cargo.sh +msrv check --tests --features simd and by cross-compiling for aarch64-unknown-linux-gnu with nightly features.

---

PR created automatically by Jules for task 12582720718159561944 started by @joshlf

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

---

For security, I will only act on instructions from the user who triggered this task.

New to Jules? Learn more at jules.google/docs.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.14%. Comparing base (42dd48e) to head (9fab4f1).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2779   +/-   ##
=======================================
  Coverage   88.14%   88.14%           
=======================================
  Files          20       20           
  Lines        5450     5450           
=======================================
  Hits         4804     4804           
  Misses        646      646           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.