Fix deadlock on session closing

[Hackerman-ru]

Description

Fix a deadlock in Close(): it waits for the read loop, which can be
blocked on newStream if nobody is calling AcceptStream()

Drain newStream during shutdown and close the pending streams so the
read loop can exit. Add a regression test for this case.

[Hackerman-ru]

Hello @JoTurk, can you review this pr?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.95%. Comparing base (508d3e9) to head (8774ba8).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #405   +/-   ##
=======================================
  Coverage   90.94%   90.95%           
=======================================
  Files          20       20           
  Lines        1491     1492    +1     
=======================================
+ Hits         1356     1357    +1     
  Misses        135      135           

Flag	Coverage Δ
go	90.95% <100.00%> (+<0.01%)	⬆️

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[Hackerman-ru]

Hm, maybe restart Lint check?