CI: use scons cache mount for building simulator and docs (#29436)

* build docker image with scons cache

* use setup

* scons cache

* added the dockerfile

* add the shell

* docs use cache

* dont pull lfs for docs

* simulator too

* dont pull the cache image

* fix inputs

* inputs

* booleans aren't supported

* bool not supported

* bool isnt supported

* fix

* readonly cache

* fix sim cache too

* respect readonly

* gitignore and move to correct folder

* also copy old

* move to tools/ci

* move to selfdrive/test

* just make the cache writable, it's discarded anyway

* minimize diff in this pr
old-commit-hash: 197460e06136f66f60e10ccefece646cb472b872

docs/docker/Dockerfile

@@ -1,4 +1,6 @@
-FROM ghcr.io/commaai/openpilot-base:latest as openpilot-docs-base
+FROM scons-cache as scons-cache
+
+FROM ghcr.io/commaai/openpilot-base:latest
 
 ENV PYTHONUNBUFFERED 1
 
@@ -29,7 +31,7 @@ COPY ./selfdrive ${OPENPILOT_PATH}/selfdrive
 COPY ./system ${OPENPILOT_PATH}/system
 COPY ./*.md ${OPENPILOT_PATH}/
 
-RUN scons -j$(nproc)
+RUN --mount=type=bind,from=scons-cache,source=/tmp/scons_cache,target=/tmp/scons_cache,rw scons -j$(nproc)
 
 RUN apt update && apt install doxygen -y
 COPY ./docs ${OPENPILOT_PATH}/docs
@@ -38,5 +40,5 @@ WORKDIR ${OPENPILOT_PATH}/docs
 RUN make html
 
 FROM nginx:1.21
-COPY --from=0  /home/batman/openpilot/build/docs/html /usr/share/nginx/html
+COPY --from=1 /home/batman/openpilot/build/docs/html /usr/share/nginx/html
 COPY ./docs/docker/nginx.conf /etc/nginx/conf.d/default.conf