feat: support BROWSER environment variable

[kricsleo]

resolves #154

Note

The current implementation only covers half the features of open, and lacks automatic platform detection for the browser.
This might not provide a good DX (users have to specify BROWSER="Google Chrome" on macOS and BROWSER=chrome in Windows). I'm hesitant to port all the implementations due to the large amount of code duplication.
Instead, should we consider simply using the open package? We could inline it during the build to avoid installing an extra package if that's a concern. WDYT? 🤔

[codecov]

Codecov Report

❌ Patch coverage is 0% with 30 lines in your changes missing coverage. Please review.
✅ Project coverage is 44.36%. Comparing base (d115045) to head (cd37db0).
⚠️ Report is 30 commits behind head on main.

Files with missing lines	Patch %	Lines
src/lib/open.ts	0.00%	29 Missing ⚠️
src/listen.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #210      +/-   ##
==========================================
- Coverage   49.42%   44.36%   -5.07%     
==========================================
  Files          17       17              
  Lines        1819     1321     -498     
  Branches      147      150       +3     
==========================================
- Hits          899      586     -313     
+ Misses        915      729     -186     
- Partials        5        6       +1     

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