Ignore __MACOSX folder in tool archives when launching core install

[alessio-perugini]

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What kind of change does this PR introduce?

This ignore __MACOSX autogenerated folder inside the archives. When we launch the core install command
if the downloaded archive, besides the root dir, contains also the __MACOSX we simply ignore that dir.

What is the current behavior?

If we encounter a __MACOSX folder we throw an error.

What is the new behavior?

We ignore every __MACOSX folder when searching for the package root.

Does this PR introduce a breaking change, and is titled accordingly?

nope

Other information

I've added a commit to propose a small refactoring feel free to revert it.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.03 ⚠️

Comparison is base (ebdef4d) 62.57% compared to head (9e4e5e0) 62.55%.

Additional details and impacted files

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##           master    #2162      +/-   ##
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Flag	Coverage Δ
unit	62.55% <100.00%> (-0.03%)	⬇️

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Impacted Files	Coverage Δ
arduino/resources/install.go	53.33% <100.00%> (+8.46%)	⬆️

... and 1 file with indirect coverage changes

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[cmaglie]

LGTM! just a missing license header.

[cmaglie]

We should also update the documentation and explicitly say that in the archives the subdirectory __MACOSX is ignored.

BTW I can't really find a place where the archive format is specified, the only place where this topic is discussed is at the bottom of docs/package_index_json-specification.md:

Installation archive structure

The installation archives contain the Board support files.

Supported formats are .zip, .tar.bz2, and .tar.gz. Starting from Arduino CLI >=0.30.0 support for .tar.xz, and
.tar.zst has been added, by the way, if you want to keep compatiblity with older versions of Arduino IDE and Arduino
CLI we recommend using one of the older formats.

The folder structure of the core archive is slightly different from the standard manually installed Arduino IDE 1.5+
compatible hardware folder structure. You must remove the architecture folder(e.g., avr or arm), moving all the
files and folders within the architecture folder up a level.

the hint for "The folder structure of the core archive" is referred specifically for platform archives. So... I guess this documentation requires a bit of refactoring, maybe it's worth opening another issue.

[alessio-perugini]

We should also update the documentation and explicitly say that in the archives the subdirectory __MACOSX is ignored.

BTW I can't really find a place where the archive format is specified, the only place where this topic is discussed is at the bottom of docs/package_index_json-specification.md:

Installation archive structure

The installation archives contain the Board support files.
Supported formats are .zip, .tar.bz2, and .tar.gz. Starting from Arduino CLI >=0.30.0 support for .tar.xz, and
.tar.zst has been added, by the way, if you want to keep compatiblity with older versions of Arduino IDE and Arduino
CLI we recommend using one of the older formats.
The folder structure of the core archive is slightly different from the standard manually installed Arduino IDE 1.5+
compatible hardware folder structure. You must remove the architecture folder(e.g., avr or arm), moving all the
files and folders within the architecture folder up a level.

the hint for "The folder structure of the core archive" is referred specifically for platform archives. So... I guess this documentation requires a bit of refactoring, maybe it's worth opening another issue.

We'll be taking care to improve docs in a separate PR. Tracking on #2167 🚀