Fix#1275, which had been closed as stale, and is now reopened pending the implementation of this PR. If there is a page break inside a defined print area, Excel may not render the print correctly unless the xml `brk` tag contains a `max` attribute. Libre Office renders it correctly. This seems like a bug in Excel (https://learn.microsoft.com/en-us/openspecs/office_standards/ms-oe376/b32ae11b-dee7-4dcb-9b46-a0feb32ce94f states that Office ignores min and max). PR #3345 (issue #3143) already addressed this problem by allowing the user to explicitly specify a `max` property in the PageBreak object. This PR eliminates the need for the user to make use of that kludge, by adding `max` to the xml whenever a page break is specified on a sheet with a defined print area. Xlsx Reader will now ignore the `max` attribute for row breaks, since it is no longer needed; it already ignores it for column breaks. The user may still set the `max` property if desired, just in case the new treatment is not adequate (I have not found a case where that is true). Two existing unit tests are very marginally changed because of this PR.
Fix#4438. Do some optimization if Excel value is an integer. This is unlikely to make much of a difference, but the use case seems pretty common (cell represents a date rather than date-time), so we may as well do it. There had been no tests for negative integer values, because Excel does not handle those well, but OpenOffice and Gnumeric handle them just fine, so add some tests for them.
Phpstan level 10 reports an enormous number of errors. So does the excluded missingType.iterableValue. I do not plan to introduce either any time soon. But I will submit piecemeal changes from time to time. Changes will be mostly limited to phpdoc type declarations.
Phpstan hasn't identified any errors in Samples in a long time. But, as it turns out, one particular error is suppressed:
```
Variable $helper might not be defined.
```
This error would be generated by almost all samples, and the errors that it suppresses will become problematic if we move to Level 10. We are not yet committed to doing that, but it is pretty easy to write a script to change the samples so that error no longer happens, and there isn't really any reason to delay doing so. The results of that script constitute this PR.
Issue #4435 was initially described incorrectly. While investigating the original description, I came upon this problem. Ods Reader is trying to set some cells to null without supplying a valid DataType to setValueExplicit, causing that method to throw an exception. Reader is changed to no longer call that method when value is null and DataType is null-string.