Windows - add a DEBUG build with debugging symbols

[EdmondDantes]

This change enables the extension to be compiled correctly in debug mode.
The issue was that, in the default case, the builder attempted to use files from the PHP DEV PACK, which lacks debug symbols. This resulted in a linker error, as it couldn't find the emalloc functions (these have different signatures in DEBUG builds).

Solution:

• Add an environment variable PHP_LIB.
• Check if we are compiling in debug mode. If so, require this variable to be set. Otherwise, proceed as before.
• PHP_LIB must point to a built PHP instance. The library name is chosen as php8ts_debug.lib.

P.S. I tried to find a place in the documentation to add this, but I can't figure out where it should go. If you can provide details, I would certainly include it.

[Xenira]

Thanks for the contribution and sorry for the delay in getting back to you.

Regarding the documentation it would probably be best to add a separate "Windows" section here as I could not find a good place to put it.

Seems like the pipeline builds are now unable to find the proper php lib. Can you have a look at that?

EDIT:

Regarding docu: Adding this to https://github.com/davidcole1340/ext-php-rs?tab=readme-ov-file#windows-requirements would probably be fine too.

[EdmondDantes]

@Xenira Thank you for the suggestions.

I fixed the library search function to ensure it works in all cases or returns an error.
I added a brief note that for DEBUG builds on Windows, PHP must be manually built from the SDK.

[EdmondDantes]

@Xenira Thanks!

[Xenira]

@EdmondDantes could you run cargo fmt on your changes?

[EdmondDantes]

@Xenira Done

[Xenira]

Updated the branch with clippy fixes from master #352