MinecraftFontAssetSource
Synchronous source of pack-relative files for an immutable font snapshot. Paths use forward slashes, including assets/namespace/path and optional pack.mcmeta. A loader retains neither this source nor any returned mutable collection or array. Implementations own no persistent open stream; callers must obey any source-specific thread contract. Custom sources must bound allocation inside their callbacks; loaders also validate returned sizes before copying. Implement MinecraftBoundedFontAssetSource to receive the current limits and stop while streaming or enumerating.