ai/live: Set idle timeout.

[j0sh]

We are accumulating hundreds of TCP connections per orchestrator on the gateways, and not having an idle timeout is probably why.

The timeout is set to 90 seconds to match the behavior of golang's default HTTP client

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 31.69886%. Comparing base (0a77ad0) to head (f43c518).
Report is 1 commits behind head on master.

Additional details and impacted files

@@                 Coverage Diff                 @@
##              master       #3670         +/-   ##
===================================================
+ Coverage   31.69242%   31.69886%   +0.00644%     
===================================================
  Files            156         156                 
  Lines          47311       47314          +3     
===================================================
+ Hits           14994       14998          +4     
+ Misses         31433       31432          -1     
  Partials         884         884                 

Files with missing lines	Coverage Δ
server/segment_rpc.go	73.03989% <ø> (ø)
trickle/trickle_publisher.go	63.50711% <100.00000%> (+0.52634%)	⬆️

... and 1 file with indirect coverage changes

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Files with missing lines	Coverage Δ
server/segment_rpc.go	73.03989% <ø> (ø)
trickle/trickle_publisher.go	63.50711% <100.00000%> (+0.52634%)	⬆️

... and 1 file with indirect coverage changes

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[j0sh]

Ready for review. The straggling connections I spotted were from trickle preconnects retrying due to my testing method of killing an active runner - see #3675 for the fix to that

[leszko]

LGTM