Improve type safety and code quality

[curry684]

Following up on the excellent work by @DannyvdSluijs in #672:

I did some testing because of my other 2 PR's regarding type safety, and it's actually pretty easy to bring the project to level 7 or even 8 in PHPstan. However, to do it right it would require breaking signatures by adding return types and parameter types. This would break B/C and therefore require a new major version be released. I think this would also be a good moment to:

• Upgrade minimum PHP to 8.2 (older are all EOL next month)
• This could potentially also be the opportune moment to remove the hard dependency on Guzzle as per PSR 18 compatibility #632 if feasible and switch to psr/http-client-implementation instead (most Symfony projects use the Symfony HTTP client nowadays)

If not we can still do a lot, but we'd be using phpdoc annotations mostly.

What are maintainer ideas on this?

[DannyvdSluijs]

I’m all for, but I’m not the maintainer. So I can’t guarantee PR acceptance. I haven’t been active here as I’ve switched projects and I’m not doing that much with Exact anymore.

I’m willing to collaborate on this as I believe my generating piece of code (repo here) could do the heavy lifting in updating all models.

[remkobrenters]

@DannyvdSluijs that would be awesome. Lets ask @stephangroen how he sees this but we (@rubenwebparking) are in favor of a major version bump opening doors to support newer technologies and stricter type casting etc. I wonder if it would be smarter to move the other PR #683 into this as well to just bring it all together to a polished new major version.

[curry684]

I'm also happy to help, I believe the best course of action would be to make a branch next in which we put the PHPstan level at 8 to begin with and then call feature stop on v4.

Both #683 and #684 are candidates for short-term merging in v4 as they have no B/C issues (only changes in PHPdoc comments, so they only affect analysis tools). If we go for v5 separately I would recommend choosing #684 over #683.