nx_av1_tile_gate.nx

nx_av1_tile_gate.nx -- proves AV1/AV2 tile geometry and tile_info. T2 pins the mode-info count against the OBVIOUS-BUT-WRONG formula. MiCols is 2 * ((w + 7) >> 3): round to 8 pixels first, THEN count 4x4 units. The natural (w + 3) >> 2 agrees on multiples of 8 and disagrees everywhere else, so the test uses 1, 4, 7, 8, 9 and 1920 -- a 1x1 frame has TWO mode-info columns, not one, and only the correct formula gives that. T3 pins ns(): small values cost w-1 bits and large ones w. Reading it as a fixed-width field consumes one bit too few on every large value. The test round-trips every value of several non-power-of-two alphabets, so a fixed-width reader cannot pass. T4 round-trips real tile_info at 1920x1080 and 3840x2160, with both 64 and 128 superblocks, across the legal log2 range. license_tier: ORIGINAL