fix: percent-encode page URLs built from file paths

A file named Müsli.html was indexed with the URL /Müsli.html, which only
resolves if the host happens to serve the same byte sequence the index was
built from. Encode the URL that build_url derives from the file path using
the URL spec's path percent-encode set, leaving / and % alone so path
separators and already-encoded filenames are unaffected.

URLs supplied by the caller (data-pagefind-meta="url:...", addCustomRecord)
do not go through build_url and are untouched.

Fixes #619

pagefind/Cargo.toml

@@ -90,6 +90,7 @@ actix-web = { version = "4", optional = true }
 actix-files = { version = "0.7", optional = true }
 lexical-core = "1.0.0"
 path-slash = "0.2"
+percent-encoding = "2"
 rayon = "1.10"
 rust-patch = "0.1.3"
 typed-builder = "0.23.2"