sc_sock: use dense events array instead of a sparse one on Windows

[svladykin]

Optimization:

• O(1) sc_sock_poll_add
• work with only count events instead of cap
• events array is not sparse anymore
• sc_sock_poll_wait returns 0 if no events were actually triggered

[codecov[bot]]

Codecov Report

Merging #91 (9e4f201) into master (0b74cbc) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #91   +/-   ##
=======================================
  Coverage   99.81%   99.81%           
=======================================
  Files          21       21           
  Lines        2192     2192           
  Branches      385      385           
=======================================
  Hits         2188     2188           
  Partials        4        4           

Impacted Files	Coverage Δ
socket/sc_sock.c	100.00% <ø> (ø)

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[svladykin]

There is a bug in this PR though: we do not update fdt->index on the moved last element. Tests do not catch it, probably need to store the pointer to the actual fdt alongside with data.

[svladykin]

Ok, this approach does not work at all in case when we delete a socket from poll inside of the event loop.