polledTimeout: add option to use CPU count instead of millis() (#5870)

* polledTimeout: add option to use CPU count instead of millis()

* use more "using" alias

* more c++/clear code, using typename (thanks @devyte)

* rename class name to include unit, introduce timeMax() and check it with assert()

* remove useless defines

* improve api readability, add micro-second unit

* update example

* mock: emulate getCycleCount, add/fix polledTimeout CI test

* + nano-seconds, assert -> message, comments, host test

* allow 0 for timeout (enables immediate timeout, fix division by 0)

* typo, set member instead of local variable

* unify error message

* slight change on checkExpired() allows "never expired"
also removed printed message, add YieldAndDelay, simplify calculations

* remove traces of debug.h/cpp in this PR

* include missing <limits> header

* back to original expired test, introduce boolean _neverExpires, fix reset(), getTimeout() is invalid

* fix expiredOneShot with _timeout==0 check

* reenable getTimeout()

* expose checkExpired with unit conversion

* fix timing comments, move critical code to iram

* add member ::neverExpires and use it where relevant

* improve clarity

* remove exposed checkExpired(), adapt LEAmDNS with equivalent

* add API ::resetToNeverExpires(), use it in LEAmDNS

* remove offending constness from ::flagged() LEAmDNS (due do API fix in PolledTimeout)

* simplify "Fast" base classes

* minor variable rename

* Fix examples

* compliance with good c++ manners

* minor changes for consistency

* add missing const

* expired() and bool() moved to iram

* constexpr compensation computing

* add/update comments

* move neverExpires and alwaysExpired

cores/esp8266/HardwareSerial.cpp

@@ -139,7 +139,7 @@ size_t HardwareSerial::readBytes(char* buffer, size_t size)
 
     while (got < size)
     {
-        esp8266::polledTimeout::oneShot timeOut(_timeout);
+        esp8266::polledTimeout::oneShotFastMs timeOut(_timeout);
         size_t avail;
         while ((avail = available()) == 0 && !timeOut);
         if (avail == 0)