Fix double deref in connection pool error path

[guhetier]

Description

When creating a connection pool, if a QuicConnStart fails:

• the connection was marked as ExternalOwner to prevent it from sending notification to the app
  • but this also mean that the closing logic will take care of releasing the owner refcount, since the application is not the owner yet
• the connection was closed using MsQuicConnectionClose, which release the refcount of the application

This caused a double release, triggering an assertion.

We should not call APIs from internal call (it makes logging confusing and breaks some assumptions), so queue the connection close manually instead.

Fixes #5550.

Testing

C/I.
Need to consider if there is a simply way to deterministically test the connection pool failure paths.

Documentation

N/A

[codecov]

Codecov Report

❌ Patch coverage is 4.54545% with 21 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.15%. Comparing base (d3d182c) to head (5e8f7bb).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
src/core/connection_pool.c	4.54%	21 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5597      +/-   ##
==========================================
+ Coverage   84.81%   85.15%   +0.33%     
==========================================
  Files          60       60              
  Lines       18647    18663      +16     
==========================================
+ Hits        15816    15893      +77     
+ Misses       2831     2770      -61     

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