Allow users to provide multiple build cache paths during compilation.

[alessio-perugini]

Describe the request

Create a new config build_cache.core.extra_paths that contains paths of other precompiled cores.

During the compilation phase the arduino-cli will look for precompiled cores present in the directories listed in the new config build_cache.core.extra_paths.

What happens when the user sets both the --build-cache-path and build_cache.core.extra_paths config ?

• the arduino-cli will always look for the extra_paths present in the config, and then the one in the --build-cache-path flag.
• In case the precompiled core doesn't exist, the write destination will be the one provided with the --build-cache-path flag

What happens when the user sets only the build_cache.core.extra_paths config ?

• the arduino-cli will always look for the extra_paths present in the config, and then the one in the default location (the temp directory).
• In case the precompiled core doesn't exist, the write destination will be the default location (the temp directory)

Describe the current behavior

Currently is not possible to read the precompiled cores from multiple path.
We can only read the in the default tmp dir, or in the provided path of --build-cache-path

Arduino CLI version

nightly

Operating system

Linux

Operating system version

23.10

Additional context

No response

Issue checklist

• I searched for previous requests in the issue tracker
• I verified the feature was still missing when using the nightly build
• My request contains all necessary details