Game loop: some minor optimizations

[theNestruo]

The Dispatcher

https://github.com/oisee/antique-toy/blob/main/chapters/ch18-gameloop/draft.md#the-dispatcher

The HL = game_state + A part can be optimized from 45T...

    ; Dispatch to current state handler (original)
    ld   a, (game_state)    ; 13T  load state index
    ld   l, a               ; 4T
    ld   h, 0               ; 7T
    ld   de, state_table    ; 10T
    add  hl, de             ; 11T  HL = state_table + offset

...to a slightly faster (42T) and slightly longer (1B):

    ; Dispatch to current state handler
    ld	hl, state_table
    ld	a, (game_state)
    add	l
    ld	l, a
    jr	nc, .else
    inc	h
.else:

Iterating Entities

https://github.com/oisee/antique-toy/blob/main/chapters/ch18-gameloop/draft.md#iterating-entities

    ; Check if entity is active
    ld   a, (ix + 9)        ; 19T  load flags byte (offset +9)
    bit  0, a               ; 8T   test ACTIVE flag
    jr   z, .skip           ; 12/7T skip if inactive

Can be rewritten as:

    ; Check if entity is active
    bit  0, (ix + 9)        ; 20T   test ACTIVE flag of flags byte (offset +9)
    jr   z, .skip           ; 12/7T skip if inactive

Saving 7T per entity (112T in total for 16 entities).

Update Dispatch by Type

https://github.com/oisee/antique-toy/blob/main/chapters/ch18-gameloop/draft.md#update-dispatch-by-type

Same optimization for HL = type_handlers + A as the one mentioned for The Dispatcher. Saves 3T per entity (48T in total for 16 entities).