Add direct type conversion on Dual

[adrhill]

Closes #164 by supporting:

• Int(d::Dual)
• Integer(d::Dual)
• Float64(d::Dual)
• Float32(d::Dual)

This currently throws an InexactError when tracers are not empty. This is analogous to ForwardDiff's approach.

Depending on the outcome of the ongoing discussion in #167, we might want to make this less conservative for Int(d) and Integer(d) in the future.

[codecov-commenter]

⚠️ Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

Attention: Patch coverage is 78.26087% with 5 lines in your changes missing coverage. Please review.

Project coverage is 91.65%. Comparing base (8587e0d) to head (eba1edc).
Report is 1 commits behind head on main.

Files	Patch %	Lines
test/test_constructors.jl	75.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #168      +/-   ##
==========================================
+ Coverage   90.25%   91.65%   +1.40%     
==========================================
  Files          37       37              
  Lines        1570     1786     +216     
==========================================
+ Hits         1417     1637     +220     
+ Misses        153      149       -4     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.