[6.1]zero timeout stream data without waiting

[NathanFreeman]

No description provided.

[matyhtf]

The zero-timeout path itself should remain nonblocking for every subsequent read, but the new regression expects the second fread() to block until the server writes. The PR's own PHP 8.4 Ubuntu CI demonstrates the contradiction: the second read correctly returns an empty string immediately and the new test fails. Please either restore a positive timeout before the second read or wait for readability before asserting the payload. This branch also needs to be updated for merged #6260: PHP_STREAM_OPTION_READ_TIMEOUT is applied to both read and write timeouts here, and the explanatory comment must be preserved.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.31%. Comparing base (bb7880e) to head (85d9355).

Additional details and impacted files

@@           Coverage Diff           @@
##              6.1    #6255   +/-   ##
=======================================
  Coverage   86.30%   86.31%           
=======================================
  Files         110      110           
  Lines       16815    16815           
  Branches     2983     2983           
=======================================
+ Hits        14513    14514    +1     
+ Misses       2302     2301    -1     

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