Fix: Normalize macro route path to ensure compatibility with Windows

[bartleboeuf]

Issue description :
The macro was generating route paths from filesystem paths without normalizing separators/leading slash on Windows, so Axum received paths like \foo and panicked.

Fixes :

• Updated EmbeddedFileInfo path handling to always normalize generated web routes via a helper.
• In route generation, relative paths are now converted to web-safe paths (backslashes --> /, ensure leading /) .
• strip_html_ext logic was working on absolute/path-string prefixes, which broke on Windows separator differences and could generate wrong routes. A quick rework of the helper is done.

All Unit tests are now good on Linux and Windows. (i was not able to test on Mac).

[bartleboeuf]

#10