`BigInt` and `BigRat`

[Alex-Fischman]

This PR adds BigInt and BigRat sorts by external demand. This PR does not add significant complexity to the codebase, as both BigInt and BigRat are implemented the same way as we've implemented Rational.

As a side effect, this PR also:

• consolidates our dependency on num for BigInt
• fixes a bug in the add_primitives macro to allow for arguments of different types
• adds a very very small test

[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #457 will not alter performance

_{Comparing Alex-Fischman:big-int (b8a0548) with main (a38edb3)}

Summary

✅ 8 untouched benchmarks

[yihozhang]

Thanks for the quick implementation! cc @rtzam

🐀