Add a function returning the brand string of the host

[alalazo]

This PR adds a function to return the brand string of the CPU:

>>> import archspec.cpu
>>> archspec.cpu.brand_string()
'11th Gen Intel(R) Core(TM) i7-1185G7 @ 3.00GHz'

It currently works on x86_64 (all platforms), and darwin (all targets family). Linux aarch64 is not covered yet.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 86.66667% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 93.92%. Comparing base (7b8fe60) to head (d8ccf8d).

Files	Patch %	Lines
archspec/cpu/detect.py	85.71%	2 Missing ⚠️

❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #156      +/-   ##
==========================================
- Coverage   94.15%   93.92%   -0.24%     
==========================================
  Files           8        8              
  Lines         496      510      +14     
==========================================
+ Hits          467      479      +12     
- Misses         29       31       +2     

Flag	Coverage Δ
unittests	93.92% <86.66%> (-0.24%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[alalazo]

For reference and context, see reframe-hpc/reframe#3132

@vkarak @jack-morrison Let me know if this works for you.

[vkarak]

Thanks @alalazo, I tested on an Intel machine and it's fine. I'll test it tomorrow on an Arm and let you know.

[alalazo]

It currently doesn't return meaningful results on ARM + linux. Only Apple Silicon.

[vkarak]

Lgtm