Implement a new DataUriLoader that handles the data: URL scheme, enabling
inline resources like <img src="data:..."> and CSS url(data:...). The loader
parses mediatype headers, supports base64 and percent-encoded data, enforces
a 10 MB size limit matching HttpLoader, and handles case-insensitive ;base64
detection and whitespace stripping per WHATWG Fetch §4.1. Percent-decoding is
applied before base64 decoding to handle url crate path encoding of /+=.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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