ci: add Docker image caching to build_all and macro_coverage jobs

[BenGardiner]

which should prevent the 'random' build failures

[github-actions]

🔨 Build & Macro Coverage Report

Default Builds — Hex File Sizes

ECU	Debug (tag 15.0)	Debug (tag 2.1.1)	Release (tag 15.0)	Release (tag 2.1.1)
ECUA	520 KiB (532736 bytes)	520 KiB (532691 bytes)	349 KiB (358103 bytes)	349 KiB (358005 bytes)
ECUB	338 KiB (346808 bytes)	338 KiB (346808 bytes)	200 KiB (205119 bytes)	200 KiB (205074 bytes)
ECUC	319 KiB (326844 bytes)	319 KiB (326844 bytes)	179 KiB (184238 bytes)	179 KiB (184177 bytes)
ECUD	329 KiB (337231 bytes)	329 KiB (337231 bytes)	186 KiB (191455 bytes)	186 KiB (191211 bytes)

Macro Coverage Build Results

Variant	Macros Changed	Result	Warnings
gsusb	+ENABLE_GSUSB	✅ Pass	0
gsusb_and_bb	+ENABLE_GSUSB +ENABLE_BITBANG	✅ Pass	0
i2c	+ENABLE_I2C	✅ Pass	0
j1939	+ENABLE_J1939_MODE	✅ Pass	0
j1939_showcase_mode	+ENABLE_J1939_MODE +RAMN_SHOWCASE_MODE	✅ Pass	0
kwp	+ENABLE_KWP	✅ Pass	0
no_debug	−ENABLE_USB_DEBUG −ENABLE_JOYSTICK_CONTROLS −ENABLE_SCREEN −ENABLE_CHIP8 −GENERATE_RUNTIME_STATS	✅ Pass	0
no_dynamic_bitrate	−ENABLE_DYNAMIC_BITRATE	✅ Pass	0
no_extras	−ENABLE_J1979 −ENABLE_MINICTF −ENABLE_CHIP8 −ENABLE_SCREEN −ENABLE_SPI	✅ Pass	0
no_uds	−ENABLE_UDS −ENABLE_UDS_REPROGRAMMING	✅ Pass	0
uart	+ENABLE_UART −ENABLE_CDC −ENABLE_USB	✅ Pass	0
usb_autodetect	+ENABLE_USB_AUTODETECT	✅ Pass	0
watchdog	+WATCHDOG_ENABLE	✅ Pass	0

Source Code Compile Coverage

• Total .c source lines: 21370
• Lines compiled in ≥1 configuration: 20014 (~94%)
• ENABLE_ macro coverage: 23/23 (100.0%) macros tested in both ON and OFF states

Full ENABLE_ Macro Coverage Table

#	Macro	Tested ON	Tested OFF	Covered
1	ENABLE_ADC	default (ECUB, ECUC, ECUD)	default (ECUA)	✅
2	ENABLE_BITBANG	default (ECUA), variant: gsusb_and_bb	default (ECUB, ECUC, ECUD)	✅
3	ENABLE_CDC	default (ECUA)	default (ECUB, ECUC, ECUD), variant: uart	✅
4	ENABLE_CHIP8	default (ECUA)	default (ECUB, ECUC, ECUD), variant: no_debug, variant: no_extras	✅
5	ENABLE_DYNAMIC_BITRATE	default (ECUA, ECUB, ECUC, ECUD)	variant: no_dynamic_bitrate	✅
6	ENABLE_GSUSB	variant: gsusb, variant: gsusb_and_bb	default (ECUA, ECUB, ECUC, ECUD)	✅
7	ENABLE_I2C	variant: i2c	default (ECUA, ECUB, ECUC, ECUD)	✅
8	ENABLE_J1939_MODE	variant: j1939, variant: j1939_showcase_mode	default (ECUA, ECUB, ECUC, ECUD)	✅
9	ENABLE_J1979	default (ECUA, ECUB, ECUC, ECUD)	variant: no_extras	✅
10	ENABLE_JOYSTICK_CONTROLS	default (ECUA)	default (ECUB, ECUC, ECUD), variant: no_debug	✅
11	ENABLE_KWP	variant: kwp	default (ECUA, ECUB, ECUC, ECUD)	✅
12	ENABLE_MINICTF	default (ECUA, ECUD)	default (ECUB, ECUC), variant: no_extras	✅
13	ENABLE_SCREEN	default (ECUA)	default (ECUB, ECUC, ECUD), variant: no_debug, variant: no_extras	✅
14	ENABLE_SPI	default (ECUA, ECUD)	default (ECUB, ECUC), variant: no_extras	✅
15	ENABLE_UART	variant: uart	default (ECUA, ECUB, ECUC, ECUD)	✅
16	ENABLE_UDS	default (ECUA, ECUB, ECUC, ECUD)	variant: no_uds	✅
17	ENABLE_UDS_REPROGRAMMING	default (ECUA, ECUB, ECUC, ECUD)	variant: no_uds	✅
18	ENABLE_USB	default (ECUA)	default (ECUB, ECUC, ECUD), variant: uart	✅
19	ENABLE_USB_AUTODETECT	variant: usb_autodetect	default (ECUA, ECUB, ECUC, ECUD)	✅
20	ENABLE_USB_DEBUG	default (ECUA)	default (ECUB, ECUC, ECUD), variant: no_debug	✅
21	ENABLE_XCP	default (ECUB, ECUC, ECUD)	default (ECUA)	✅
22	GENERATE_RUNTIME_STATS	default (ECUA, ECUB, ECUC, ECUD)	variant: no_debug	✅
23	WATCHDOG_ENABLE	variant: watchdog	default (ECUA, ECUB, ECUC, ECUD)	✅

[BenGardiner]

regarding versions:

1. _version.sh / .bat contents will always be built as a version.
2. CI workflows will additionally test other versions included in teh yaml ("15.0" right now)