test(macro): add test infrastructure for macro crate

[Xenira]

Fixes: #530

Description

This allows us to test macro expansion by:

1. calling cargo expand on the test files and comparing the output
2. Expanding the macros at runtime to get coverage

Checklist

Check the boxes that apply (put an x in the brackets, like [x]). You can also check boxes after the PR is created.

• I have read the contribution guidelines.
• I have added tests that prove my code works as expected.
• I have added documentation if applicable.
• I have added a migration guide if applicable.

❤️ Thank you for your contribution!

[coveralls]

Pull Request Test Coverage Report for Build 16393729291

Details

• 5 of 43 (11.63%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+1.0%) to 25.766%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
crates/macros/src/lib.rs	5	43	11.63%

Totals
Change from base Build 16392821488:	1.0%
Covered Lines:	992
Relevant Lines:	3850

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 16393951015

Details

• 5 of 43 (11.63%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+1.0%) to 25.766%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
crates/macros/src/lib.rs	5	43	11.63%

Totals
Change from base Build 16392821488:	1.0%
Covered Lines:	992
Relevant Lines:	3850

---

💛 - Coveralls