Path separator fix windows

[samansmink]

Changes

This PR fixes #7723 The problem was that the path separator function was static, which meant that path separator on windows would always be '' on windows which failed on hive partitioned writes.

To fix this, an API change to the FileSystem class was made: some methods are now no longer static. Also the PathSeparator call now requires a path to determine the path separator. This broke the spatial extension, so I decided to also added the same patching mechanism we added for duckdb-wasm in #7926 Check out the READMEs I added in .github/patches/*/README.md for details on the patching mechanism. TLDR; when adding change to duckdb that breaks either an extension built with duckdb CI or duckdb-wasm, you can add a patch to ensure duckdb CI passes, enabling a cleaner workflow.

I tried setting up the test server to catch this issue in CI, but there's a whole world of hurt in setting up the minio on windows ci too which would just get a bit too messy. I left it out of this PR for that reason. I did test this on windows manually and have confirmed it now works.

Follow ups

1. For testing s3 on windows, I think we should set up a job in nightly which has a real S3 token to some test bucket we own. Then this can run actualy tests against S3. As long as we keep tests reasonable this would allow actually testing this from all platforms and also have the benefit of testing against AWS S3 itself. Other services like Azure can then also be tested in similar fashion

2. The patch should be applied to the spatial extension.

[Mause]

Are you able to fix this for fsspec as well while you're at it? There's a test that should fail if it's worked

[Mause]

Specifically this one:

duckdb/tools/pythonpkg/tests/fast/test_filesystem.py

Line 195 in 0238f94

if sys.platform == 'win32' else

[Mytherin]

Looks great, thanks!