quic: fix segfault after fragmented client hello

[pimterry]

If the client hello is fragmented across packets, we start trying to initialize the application before ALPN actually selected an application, so we segfault (repro in the test here).

This changes QUIC session setup to defer processing until an application is selected (i.e. ALPN resolved). Test confirms that session handling after deferring that works fine.

[nodejs-github-bot]

Review requested:

• @nodejs/quic

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.13%. Comparing base (6572cf5) to head (d491638).
⚠️ Report is 20 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #64720      +/-   ##
==========================================
- Coverage   90.13%   90.13%   -0.01%     
==========================================
  Files         741      743       +2     
  Lines      242251   242324      +73     
  Branches    45615    45637      +22     
==========================================
+ Hits       218355   218413      +58     
- Misses      15396    15430      +34     
+ Partials     8500     8481      -19     

see 54 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/75141/