fix: resolve types relative to custom tsconfig path

[danielroe]

🔗 Linked issue

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

We now support a custom tsconfig path, but in that PR I neglected to ensure that the paths were resolved relative to the custom path if it were in a different directory.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[codecov]

Codecov Report

Merging #1041 (8ea96e0) into main (a6ce587) will increase coverage by 0.18%.
The diff coverage is 28.57%.

@@            Coverage Diff             @@
##             main    #1041      +/-   ##
==========================================
+ Coverage   67.20%   67.38%   +0.18%     
==========================================
  Files          62       62              
  Lines        6287     6280       -7     
  Branches      707      707              
==========================================
+ Hits         4225     4232       +7     
+ Misses       2049     2034      -15     
- Partials       13       14       +1     

Impacted Files	Coverage Δ
src/build.ts	41.58% <28.57%> (+2.41%)	⬆️

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