Add PageNotFoundException

[vjik]

Q	A
Is bugfix?	❌
New feature?	✔️
Breaks BC?	✔️

[what-the-diff]

PR Summary

• New 'PageNotFoundException' Class Added
  A new class named 'PageNotFoundException' has been created in the Paginator source code. This will handle scenarios where a page is not found during pagination.

• Improved Parameter Annotations in Keyset and Offset Paginators
  The KeysetPaginator and OffsetPaginator source files have new annotations to enhance code clarity and predictability. These indicate the type of variables and the expected return values of the methods. In particular, the annotations make clear that certain values should be positive or non-negative integers.

• Switched Exception Handling to Use New Class
  The use of the older 'PaginatorException' class has been replaced with the new 'PageNotFoundException' class in the 'read()' and 'isOnFirstPage()' methods within various Paginator files, offering more specific and accurate exception handling.

• Update to Test Expectations
  In the testing file 'OffsetPaginatorTest.php', the expected exceptions in multiple methods are now aligned with the newly introduced 'PageNotFoundException' class. Further, a test that was previously expected to throw an exception, testGetCurrentPageCannotBeLargerThanMaxPages, has been revised to now include an assertion for 'getCurrentPageSize()'.

• Added Return Type for 'count' Method in CountableDataInterface File
  The count() method in the 'CountableDataInterface' now has an annotation to denote that it should return a non-negative integer. This enhances code clarity by specifying the expected behavior.