Pass null to $microseconds for null $seconds

[TysonAndre]

Passing null seconds and non-null microseconds will become deprecated in php 8.1.
See https://github.com/php/php-src/pull/6879/files#r615680892 of php/php-src#6879

[staabm]

Lgtm - thanks

[codecov]

Codecov Report

Merging #88 (563a116) into master (0c99442) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master      #88   +/-   ##
=========================================
  Coverage     99.74%   99.74%           
+ Complexity      111      110    -1     
=========================================
  Files             7        7           
  Lines           397      397           
=========================================
  Hits            396      396           
  Misses            1        1           

Impacted Files	Coverage Δ
lib/Loop/Loop.php	100.00% <100.00%> (ø)

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[TysonAndre]

This is ready for another look - it requires two calls (or a variable length argument list) because php 7 doesn't allow passing in null to microseconds, but php 8 deprecates passing anything other than null to the optional parameter microseconds (tv_usec) when seconds (tv_sec) is null

https://php.net/stream_select

[TysonAndre]

php 8.1.0alpha2 is out

@staabm this could use another look

[phil-davis]

Rebased to run the current GitHub workflows CI, which runs unit tests in all versions of PHP. Everything is passing.