add cacheDir option

[danslo]

Very cool project, nice job!

I noticed that create a new instance of the runtime takes ~300ms.
There appears to be a build cache but as far as I understand this is per process, so the first New call will always do a compilation.

Just wondering what your thoughts are on a persistent build cache?

Before:

After:

340ms -> 70ms

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.75%. Comparing base (903b8b5) to head (8aa2857).
⚠️ Report is 7 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff            @@
##           master      #23    +/-   ##
========================================
  Coverage   99.74%   99.75%            
========================================
  Files          15       15            
  Lines        3576     2816   -760     
========================================
- Hits         3567     2809   -758     
+ Misses          5        3     -2     
  Partials        4        4            

Files with missing lines	Coverage Δ
options.go	100.00% <ø> (ø)
runtime.go	99.03% <100.00%> (+0.25%)	⬆️

... and 13 files with indirect coverage changes

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• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[ngocphuongnb]

@danslo Thanks a lot for the contribution!
The persistent cache idea and the performance improvement look great. Could you also update the tests to cover the new CacheDir option?

[danslo]

@ngocphuongnb Done! I think... :)

[ngocphuongnb]

@danslo The PR has been merged, thanks a lot for the contribution!