Coming from https://github.com/ramsey/uuid/pull/603, this is an attempt
to fix the errors raised by the current phpstan settings.
I went through each of the errors raised by phpstan with the following
approach.
- If a method is part of an `@immutable` class, we can consider it pure,
assuming it only affects internal variables.
- If a potentially pure method is calling a class's method that is only
swapped during testing (and not during normal usage), then we can
consider the calling method pure.
- If a class is marked deprecated, don't bother with attempting to mark
it pure or immutable.
The following are deprecated:
* `Ramsey\Uuid\Codec\OrderedTimeCodec`
* `Ramsey\Uuid\Codec\TimestampFirstCombCodec`
* `Ramsey\Uuid\Codec\TimestampLastCombCodec`
* `Ramsey\Uuid\Generator\CombGenerator`
Rename `Type\IntegerValue` to `Type\Integer`. It was originally named
`IntegerValue` because static analysis sees `Integer` in docblock
annotations and treats it as the native `int` type. `Integer` is not a
reserved word in PHP, so it should be named `Integer` for consistency
with other types in this library. When using it, a class alias prevents
static analysis from complaining.