fix(core): properly check paths during config loading on Windows

[xHeaven]

PR #1535 changed the vendor path check from /vendor/ to DIRECTORY_SEPARATOR . 'vendor' . DIRECTORY_SEPARATOR to fix Windows discovery.

Later, PR #1954 added Path\normalize to scan(), which converts all paths to forward slashes. This made the DIRECTORY_SEPARATOR check never match on Windows (it looks for \vendor\ in forward-slash paths), so vendor configs get the same priority as user configs and overwrite them via strcmp ordering.

Fixes #1982.

[github-actions]

Benchmark Results

Comparison of config-loading against 3.x (ba925951610e8987599a77663e7d8e779b8af89d).

Open to see the benchmark results

No benchmark changes above ±5%.

_{Generated by phpbench against commit e67d605}

[NeoIsRecursive]

Im thinking there should be a test for this so there isnt any regressions again. (I dont use Windows anymore, otherwise id try to help with it 😅)

slightly unrelated but the path normalizations should probably be highlighted more in the docs, so people dont use the php constants etc?