code style: use @splat where possible

As of Zig 0.14.0, `@splat` can be used for array types, which eliminates
a lot of redundant syntax and makes things generally cleaner.

I've explicitly avoided applying this change in the renderer files for
now since it would just create rebasing conflicts in my renderer rework
branch which I'll be PR-ing pretty soon.

src/datastruct/cache_table.zig

@@ -70,7 +70,7 @@ pub fn CacheTable(
         /// become a pointless check, but hopefully branch prediction picks
         /// up on it at that point. The memory cost isn't too bad since it's
         /// just bytes, so should be a fraction the size of the main table.
-        lengths: [bucket_count]u8 = [_]u8{0} ** bucket_count,
+        lengths: [bucket_count]u8 = @splat(0),
 
         /// An instance of the context structure.
         /// Must be initialized before calling any operations.