optimisation: set `enum` types explictly to `uint8_t`

[gudnimg]

This commit produces the same savings as the compiler option -fshort-enums. Except by setting the types manually we save also 2 bytes of SRAM.

By default, the enum type is 2 bytes, we can explicitly set it to one byte when applicable to reduce code size.

Almost all the savings come from enum Mode in leds.h.

Change in memory: Flash: -116 bytes SRAM: -2 bytes

[github-actions[bot]]

All values in bytes. Δ Delta to base

ΔFlash	ΔSRAM	Used Flash	Used SRAM	Free Flash	Free SRAM
-116	-2	28254	1667	418	893