Description:
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PHP has supported fractional seconds apparently dating back to 5.2.2 - a bit over 13 years. However when trying to create a new DateTime or DateTimeImmutable object from a unix timestamp (via "@1591858149"), non-integer timestamps are not parsed and can throw an exception:  Exception: DateTime::__construct(): Failed to parse time string (@1591858149.085) at 

Since `new DateTime()` will have a fractional component set based on the system clock, and other constructor formats support it (example: https://www.php.net/manual/en/class.datetime.php#118608), this inconsistency seems specific to unix timestamps and should be resolved



Test script:
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https://3v4l.org/54J1b

<?php

$timestamp = 1591858149.085;
$dt = new DateTime("@$timestamp");
$dti = new DateTimeImmutable("@$timestamp");

Expected result:
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No errors; created objects correctly store the microseconds component from the timestamp.

Actual result:
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Exception was thrown.