Follow the VIC-II sprite counters per cycle and draw per-line sprites from them

[highbyte]

Summary

• The VIC-II keeps each sprite's data counter, its base and the expansion flip-flop as the chip does, with the checks in cycles 15, 16, 55, 56 and 58 applied as the raster advances. A change of the Y-expand bit lands before or after the cycle 55 check according to its own cycle, clearing the bit sets the flip-flop at once, and the DMA ends when the counter base reaches 63. That gives the 23-line sprite of VICE's d017 tests and the sprite stretcher of the demos. The bus stall model anticipates the compare that starts a sprite.
• With per-line sprites on, the sequencer pixel generator draws each raster line's sprites from the bytes the chip fetched for it instead of a band captured at the sprite's start, so pointer, data, position and expansion changes mid-sprite show on the line they reach. The frame-level sprite path and the legacy generator are unchanged.
• Performance: the sprite events skip all work while no sprite is enabled or fetching and are applied behind one compare per raster advance; the model's per-line constants are cached instead of fetched through abstract properties on every advance; the generator counts its line and cycle along instead of dividing per cycle.
• New sample SpriteStretch (a diamond stretched by a wave through per-line $D017 writes, in a bad-line-free band). Two sprite-only demos in Download & Run, For Your Sprites Only and Unfortunate Coincidence, with a requiresPerLineSprites flag that switches per-line sprites on for a program.

Validation

• 467 C64 tests, full suite 2935 passed, 9 skipped. New tests: Vic2SpriteDmaTests (compare and display cycles, 21 and 42 rows, expand bit cleared mid-sprite before and after the cycle 55 check, hold and release of a row, redisplay by a rewritten Y) and a per-line render test of the d017 case.
• VICE test programs: spritedma 4/4 on PAL and NTSC (were 0/4); 113 tests across ten suites with the same 18 known differences as before (videomode residuals, gfxfetch, disable-bad).
• Commando (two snapshots, D64 PAL and NTSC) and Giana Sisters (D64 PAL and NTSC) render byte-identical to the integration branch; one 60-frame Commando run differs by 4 pixels where a sprite's last row is now clipped by its own line's border span.
• Frame benchmark on the integration branch and this branch, alternating (MacBook Air M1, .NET 10.0.203): without sprites level within the run-to-run spread; with eight visible sprites +3 to +9%, the counters and fetch state of fetching sprites per line.
• SonarCloud branch analysis clean at Major and above.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud