refactor!: improve library

[DamianGlowala]

This PR:

• makes API functions' return values consistent (avoids suppressing errors thrown by execa or returning {})
• cleans up the test/ folder
• addresses workspace arg handling based on the package manager with corresponding tests
• ensures error gets thrown when package manager auto-detection fails to find any
• organises util functions into separate files in the utils/ directory
• marks addDevDependency as deprecated (either we should provide equivalent removeDevDependency or might be better to delete it entirely) - open to opinions, but knowing this is as simple as addDependency(name, { dev: true }) makes me think if we should get rid of it in a major release
• adds includeParentDirs option to detectPackageManager util function, which prevents from bubbling the search up if not set to true explicitly
• resolves https://github.com/unjs/nypm/issues/53

@pi0, are segmentation faults when using corepack with npm on ubuntu worth reporting? Will revert to the initial workaround for now anyway.

[codecov[bot]]

Codecov Report

Merging #75 (b953c10) into main (0e22f7f) will increase coverage by 1.48%. The diff coverage is 98.85%.

@@            Coverage Diff             @@
##             main      #75      +/-   ##
==========================================
+ Coverage   96.53%   98.02%   +1.48%     
==========================================
  Files           5        5              
  Lines         289      405     +116     
  Branches       34       64      +30     
==========================================
+ Hits          279      397     +118     
+ Misses         10        8       -2     

Files Changed	Coverage Δ
src/api.ts	95.94% <98.05%> (+1.05%)	:arrow_up:
src/_utils.ts	98.42% <98.42%> (ø)
src/index.ts	100.00% <100.00%> (ø)
src/package-manager.ts	100.00% <100.00%> (ø)
src/types.ts	100.00% <100.00%> (ø)

[AndreyYolkin]

LGTM

[pi0]

Thanks so much for the time put into this PR dear @DamianGlowala ❤️

I have put a few refactors to keep the repo simplified and this mergeable.

There are really nice changes and i don't want to miss them but i couldn't do it without making a breaking change release and we lack proper changelog... therefore i ask you to please next times, consider smaller mergable PRs 🙏🏼