Correct arithmetic coder interval normalisation

[danieleades]

Summary

• initialise the arithmetic coding state with an inclusive upper bound
• restore the implicit top bit during encoder and decoder renormalisation steps

Testing

• cargo test

---

https://chatgpt.com/codex/tasks/task_e_68f3f919b6d0832abd98e68b1e637c31

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.28%. Comparing base (69a3621) to head (b6c919f).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #106   +/-   ##
=======================================
  Coverage   76.28%   76.28%           
=======================================
  Files          11       11           
  Lines         565      565           
=======================================
  Hits          431      431           
  Misses        134      134           

☔ 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.