fix: handle paused parser on socket end (issue #5360)

[mcollina]

Remove assert(!this.paused) from Parser.finish() so that when the HTTP/1
parser is paused under backpressure (body not consumed) and the socket
ends (FIN), the parser can finish gracefully instead of throwing an
uncatchable AssertionError from the socket 'end' handler.

llhttp_finish() already handles paused state by returning ERROR.PAUSED,
which is handled in the existing code path by setting this.paused = true
and returning null.

Fixes #5360

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.27%. Comparing base (313f4e0) to head (23d2064).
⚠️ Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5389      +/-   ##
==========================================
+ Coverage   93.24%   93.27%   +0.03%     
==========================================
  Files         110      110              
  Lines       36719    36751      +32     
==========================================
+ Hits        34238    34279      +41     
+ Misses       2481     2472       -9     

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