ci: Add native Apple Silicon (m1) executor

[axic]

Fixes #709.

[axic]

This task failed: https://app.circleci.com/pipelines/github/wasmx/fizzy/7204/workflows/2386fdfd-78ad-4576-b2b0-781280e6b41b/jobs/67260

Job was rejected because resource class macos.m1.large.gen1, image default is not a valid resource class

According to https://circleci.com/docs/using-macos/#available-resource-classes unfortunately we can't use these:

The macos.x86.metal.gen1 resource requires a minimum 24-hour lease. See the Dedicated Host for macOS page to learn more about this resource class.

The large and macos.m1.large.gen1 resource classes are only available for customers with an annual contract. Open a support ticket if you would like to learn more about our annual plans.

[codecov]

Codecov Report

Merging #853 (6d7c5cd) into master (b9e1c18) will increase coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #853      +/-   ##
==========================================
+ Coverage   99.15%   99.21%   +0.05%     
==========================================
  Files          87       89       +2     
  Lines       12316    13323    +1007     
==========================================
+ Hits        12212    13218    +1006     
- Misses        104      105       +1     

Flag	Coverage Δ
rust	98.48% <ø> (?)
spectests	89.78% <ø> (ø)
unittests	99.15% <ø> (ø)
unittests-32	99.25% <ø> (?)

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

see 10 files with indirect coverage changes