Use extracted signCount local in encodeV2

[Firehed]

Codecs\Credential::encodeV2 extracts $signCount alongside $rawId and $rawCbor, then calls $credential->getSignCount() again in the sprintf instead of using it. No behavior change; the local is now used the way the two adjacent ones are.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.48%. Comparing base (9d4d0fe) to head (e1a4b9f).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #104   +/-   ##
=========================================
  Coverage     81.48%   81.48%           
  Complexity      343      343           
=========================================
  Files            33       33           
  Lines           994      994           
=========================================
  Hits            810      810           
  Misses          184      184           

☔ View full report in Codecov by Harness.
📢 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.