chore: use install executable to obtain libpact

[matthewshirley]

Summary

This PR changes the installation to process by asking users to run the install executable that grabs the appropriate libpact. This is installed to the user library path.

[codecov-commenter]

Codecov Report

Merging #3 (3775519) into main (76fd662) will increase coverage by 0.34%.
The diff coverage is 80.00%.

❗ Current head 3775519 differs from pull request most recent head a1f16c0. Consider uploading reports for the commit a1f16c0 to get more accurate results

@@            Coverage Diff             @@
##             main       #3      +/-   ##
==========================================
+ Coverage   84.88%   85.22%   +0.34%     
==========================================
  Files           8        8              
  Lines         172      176       +4     
==========================================
+ Hits          146      150       +4     
  Misses         26       26              

Impacted Files	Coverage Δ
lib/src/ffi/dylib.dart	76.92% <80.00%> (+10.25%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 76fd662...a1f16c0. Read the comment docs.