Fix ParsedURL handling of %2F in URL paths

See the new extensive doxygen in `url.hh`.
This fixes fetching gitlab: flakes.

Paths are now stored as a std::vector of individual path
segments, which can themselves contain path separators '/' (%2F).
This is necessary to make the Gitlab's /projects/ API work.

Co-authored-by: John Ericson <John.Ericson@Obsidian.Systems>
Co-authored-by: Sergei Zimmerman <sergei@zimmerman.foo>

src/libstore/store-reference.cc

@@ -48,13 +48,11 @@ StoreReference StoreReference::parse(const std::string & uri, const StoreReferen
         auto parsedUri = parseURL(uri, /*lenient=*/true);
         params.insert(parsedUri.query.begin(), parsedUri.query.end());
 
-        auto baseURI = parsedUri.authority.value_or(ParsedURL::Authority{}).to_string() + parsedUri.path;
-
         return {
             .variant =
                 Specified{
                     .scheme = std::move(parsedUri.scheme),
-                    .authority = std::move(baseURI),
+                    .authority = parsedUri.renderAuthorityAndPath(),
                 },
             .params = std::move(params),
         };