Fix pfscorebars for four players

[brpocock]

The playfield score bars need to be fixed to properly support four-player mode.

Current Issue:
The pfscorebars system currently only supports players 1 and 2. Players 3 and 4 health bars are not implemented.

Current Implementation:

• UpdatePlayer1HealthBar - updates pfscore1 for player 1
• UpdatePlayer2HealthBar - updates pfscore2 for player 2
• HealthBarSystem.bas line 10: "P3/P4 health will be implemented separately"
• FrameBudgeting.bas references UpdateHealthBarPlayer0-3 functions

Investigation Needed:

• Review how pfscorebars are currently implemented in Source/Routines/HealthBarSystem.bas
• Check FrameBudgeting.bas for existing UpdateHealthBarPlayer0 and UpdateHealthBarPlayer3 functions
• Determine how to display players 3 and 4 health bars (may need different approach than pfscore1/pfscore2)
• Verify all four players have proper score bar rendering in 4-player mode
• Check if player 3 and player 4 score bars are correctly positioned and displayed
• Ensure score bar colors match player colors in 4-player mode

Related Files:

• Source/Routines/HealthBarSystem.bas - main health bar system
• Source/Routines/FrameBudgeting.bas - frame-budgeted health bar updates
• Source/Common/MultiSpriteKernel.s - kernel score rendering
• Source/Routines/GameLoopMain.bas - game loop health bar updates

Technical Notes:

• Multisprite kernel uses pfscore1 and pfscore2 registers
• Players 3 and 4 may need alternative rendering method (playfield graphics, sprites, or different score registers)
• Health bars use 8-pixel bit patterns (0-8 pixels filled from right to left)
• Health thresholds: 12, 24, 36, 48, 60, 72, 84 (split on 12s)

[brpocock]

Optimized the binary to BCD conversion routine used for P3/P4 health display in the score area. Replaced the slow BASIC loop with a fast assembly implementation using the 6502 double-dabble algorithm with decimal mode arithmetic. This provides orders-of-magnitude performance improvement for the health-to-BCD conversion used in UpdatePlayer34HealthBars.

[brpocock]

Correction: My previous comment about BCD optimization was incorrectly posted on this issue. The BCD conversion optimization is unrelated to the P3/P4 health bar implementation work described here. I've created a separate issue #1116 for that optimization.