quic: extract transport logic from Application to Session

[pimterry]

Extracting out some standalone refactoring from #63995 for easier review while we keep debating the API. I think this is a helpful refactoring generally, but especially in a world where we're restructuring Application.

This shrinks the application layer by moving generic QUIC logic that will be used by all implementations into the Session itself, and makes the Session act as a clean interface over ngtcp2 - so that the Application exclusively uses Session methods for all connection manipulation, instead of managing ngtcp2 directly. This gives a cleaner split between the low-level QUIC behaviour and the per-application-protocol layer.

There's two small fixes notably included in the migration, contained within the moved code:

• This fixes a SendPendingData bug where datagrams would stall and never send on an idle connection, in the nwrite == 0 branch.
• We now check is_destroyed() after StreamCommit, since it calls JS callbacks which could destroy the session.

[nodejs-github-bot]

Review requested:

• @nodejs/quic

[pimterry]

@jasnell Most comments handled here, and rebased onto main which had a conflict from #64303..

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.25%. Comparing base (f91697a) to head (fa84d48).
⚠️ Report is 26 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #64127      +/-   ##
==========================================
- Coverage   92.04%   90.25%   -1.80%     
==========================================
  Files         381      741     +360     
  Lines      169461   240976   +71515     
  Branches    25975    45393   +19418     
==========================================
+ Hits       155983   217488   +61505     
- Misses      13188    15069    +1881     
- Partials      290     8419    +8129     

see 487 files with indirect coverage changes

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[nodejs-github-bot]

CI: https://ci.nodejs.org/job/node-test-pull-request/74661/ 💚

[nodejs-github-bot]

Landed in 0792ee5