fix: use shared idle tracker for relay connections

[dolonet]

Summary

Fixes #423 — media downloads broken in v2.2.5 due to per-direction idle timeout.

connIdleTimeout (introduced in #420) set ReadDeadline/WriteDeadline independently for each direction. During media downloads, the client→telegram direction is idle at the application level while telegram→client is actively streaming. After IdleTimeout (default 1 min), the idle direction's ReadDeadline fires, which tears down the relay and kills the transfer.

The current behavior doesn't match the IdleTimeout documentation:

"if we have any message which will pass to either direction, a timer is reset"

The actual implementation tracked each direction independently — activity in one direction did not prevent timeout in the other.

Fix

Replace the per-direction timeout with a shared idleTracker — one atomic timestamp per connection pair. Both pump goroutines update it on any successful Read/Write. When ReadDeadline fires on an idle direction, we check the shared tracker: if the other direction was recently active, retry instead of closing.

The connection is torn down only when both directions are idle for the full timeout period — matching the documented contract.

Overhead

• One atomic.Int64 (8 bytes) per connection pair
• One atomic.Store (~1 ns) per Read/Write with data
• Zero extra goroutines
• Retry loop on idle direction wakes at most once per timeout period

Test plan

• All existing tests pass
• Verify media downloads work with default 1-min idle timeout
• Verify idle connections still get cleaned up after timeout

[9seconds]

Да, спасибо. Заняло где-то с минуту понять, в чем же оригинальная проблема, но кажется фикс корректный

[9seconds]

Могу я попросить вас добавить тест в conns_internal_test?

[dolonet]

Добавил — IdleTrackerTestSuite и ConnIdleTimeoutTestSuite в conns_internal_test.go. Покрыл основные кейсы: жизненный цикл трекера, retry при таймауте когда другое направление активно, закрытие при реальном idle, и shared tracker между двумя соединениями.

[9seconds]

Спасибо! Я сейчас тогда соберу новый PGO (на горячем пути все-таки) и сделаю релиз